2. 22
EMULSIONSEMULSIONS
• Definition
• Classification
• Applications
• Theory of emulsification
• Additives for formulation of emulsion
• Formulation of emulsions
• Emulsification techniques
• Stability of emulsions
• Evaluation of emulsions
3. 33
What is an emulsion ??What is an emulsion ??
An emulsion is a thermodynamically
unstable system consisting of at least two
immiscible liquid phases one of which is
dispersed as globules in the other liquid
phase stabilized by a third substance
called emulsifying agent.
The droplet phase is called the dispersed
phase or internal phase and the liquid in
which droplets are dispersed is called the
external (continuous phase).
6. 66
• 1. Macroemulsions (Simple Emulsions) :
• i. Oil in water (o/w) : Oil droplets are dispersed in a
continuous aqueous phase. a hydrophilic emulsifier is
used. These are preferred for oral/ IV administration and
cosmetics . These are useful as water washable drug
bases.
• ii. Water in oil (w/o) : Aqueous droplets are dispersed in
continuous oily phase. . a lipophillic emulsifier is used.
These are used for cosmetics. The are employed for
treatment of dry skin and emollient applications.
7. 77
• 2. Multiple emulsions :
• They are developed with a view to delay the release of an
active ingredient. They have three phases. They may be
oil-in-water-in-oil (o/w/o) or of water-in-oil-in-water
(w/o/w). An emulsifier is present to stabilize the
emulsions and various ionic and nonionic surfactants are
available for this purpose. Lipophilic (oil-soluble, low HLB)
surfactants are used to stabilize w/o emulsions, whereas
hydrophilic (water-soluble, high HLB) surfactants are
used to stabilize o/w systems In these emulsions within
emulsions any drug present in innermost phase must
now cross two phase boundaries to reach the external
continuous phase.
8. 88
• Preparation of multiple emulsions :
• Aqueous phase is added to oily phase, containing a
lipophilic surfactant. Upon mixing a w/o emulsion is
formed.
• This w/o emulsion is then poured into a second aqueous
solution , containing a hydrophilic surfactant. Upon mixing
multiple emulsion w/o/w is formed.
• Types of multiple emulsions : w/o/w , o/w/o
10. 1010
• 3. Microemulsions: ( diameter <0.1 um)
• They may be defined as dispersions of insoluble
liquids in a second liquid that appears clear and
homogenous to the naked eye.
• They are frequently called solubilized systems because
on a macroscopic basis they seem to behave as true
solutions.
• They are used for both internal and external formulations
and show better bioavailability than conventional
emulsions.
11. 1111
MicroemulsionsMicroemulsions
• Microemulsions are thermodynamically stable
optically transparent , mixtures of a biphasic oil –
water system stabilized with surfactants.
Microemulsion Emulsion
Transparent Yes No
Size < 0.1 µ 0.1 – 100 µ
Formation Easily dispersed Require vigorous
shaking
Stability Thermodynamically
stable
Thermodynamically
unstable
Viscosity Less viscous More viscous
12. 1212
Factors affecting type ofFactors affecting type of
emulsionemulsion
Type of emulsifying agent used
Phase volume ratio
Viscosity of each phase
13. 1313
Pharmaceutical Applications ofPharmaceutical Applications of
emulsionsemulsions
• Oral products
It covers the unpleasant taste
Increases absorption rate
• Parenteral use emulsion
i/v nutrients
i/m – depot effect
• Topical use :
Washable
Acceptable viscosity
Less greasy
Moisturizer/emollient
14. 1414
Theory of emulsificationTheory of emulsification
Droplets can be stabilized by three methods
i. Surface tension theory
ii. Oriented- wedge theory
iii. Plastic film theory
15. 1515
Emulsifying agentsEmulsifying agents
• Added to an emulsion to prevent the
coalescence of the globules of the
dispersed phase.
• Help in emulsion formation by
Reduction in interfacial tension – thermodynamic
stabilization
Formation of a rigid interfacial film – mechanical
barrier to coalescence
16. 1616
Classification of emulsifyingClassification of emulsifying
agentsagents
• Synthetic
• Surface active agents ( Monomolecular
films)
• Semi synthetic and natural
• Hydrophilic colloids ( Multimolecular films)
• Finely divided solid particles ( Particulate
film)
17. 1717
Synthetic surface active agentsSynthetic surface active agents
Description :
• Reduce interfacial tension and make the
emulsion thermodynamically more stable.
• Form protective monomolecular film
18. 1818
Synthetic surface active agentsSynthetic surface active agents
Monomolecular adsorptionMonomolecular adsorption
Oil
Rule of Bancroft : Type of emulsion is a function of relative solubility of
surfactant . The phase in which it is soluble becomes the continuous
phase
22. • Anionic surfactants
• Soaps
• 1) Monovalent
• E.g. potassium, sodium, ammonium salts of oleic acid .
They are soluble in water and are good o/w emulsifying
agents.
• Disadvantages :
• They are irritating to the GIT.. So they are useful only for
external use emulsions.
• They have a high pH, so cannot be applied on broken
skin.
23. • Anionic surfactants
• Soaps
• 2) Polyvalent
• The calcium, magnesium and aluminum salts of fatty
acids ( metallic soaps) are water insoluble and give w/o
emulsion.
• 3) Organic Soaps
• Triethanol amine soaps of fatty acids give o/w emulsion.
• They are used for external use emulsions. They are less
alkaline as compare to monovalent/polyvalent soaps so
they can be used on broken skin.
24. • Anionic surfactants
• Sulphates
• They are neutralized esters of sulphuric acid and fatty
alcohols. Poor o/w E.A if used alone. They can be used
as auxiliary emulsifying agents. E.g Sodium lauryl
sulphate
• Sulfonates
• Large group of surfactants used as detergents and
wetting agent
• Very rarely used in pharmaceutical preparations.
25. • Cationic surfactants
• They are mainly used in external preparations.
Quaternary ammonium compounds such as cetrimide,
benzalkonium chloride and benzethonium chloride are
examples of important cationic surfactants.
• These compounds besides having good antibacterial
activity are used in combination with secondary
emulsifying agents to produce o/w emulsions for external
application.
• Cetrmide emulsifying wax ( 10% cetrimide + 90%
cetosterylalcohol) produces a stable emulsion
26. – NON IONIC surfactants
• They are the class of surfactants widely used as
emulsifying agents.
• They are extensively used to produce both o/w and w/o
emulsions for internal as well as external use.
27. – NON IONIC surfactants
• Advantages : They are not effected by pH change and
presence of electrolytes.
• They also show low irritancy as compared to other
surfactants.
• Most commonly used nonionics are
• glyceryl esters (auxillary E.A)
• sorbitan fatty acid esters (spans) w/o
• polyoxyethylene derivatives of sorbitan fatty acid esters
(Tweens or polysorbates) o/w
• Polyoxyethylene / polyoxypropylene block polymers
(Macrogol) o/w emulsions used for IV
29. 2929
Hydrocolloid Emulsifying agentsHydrocolloid Emulsifying agents
Description
- Provide a protective sheath
(Multimolecular films )around the droplets
- Swell to increase the viscosity of the
system ( so that droplets are less likely to
change.)
30. 3030
Classification ofClassification of HydrocolloidHydrocolloid
emulsifying agentsemulsifying agents
Semi synthetic ( Multi molecular films)
Methyl cellulose
Carboxy methyl cellulose
. They are used for formulating o/w type
of emulsions. They primarily act by
increasing the viscosity of the system.
32. 3232
Classification ofClassification of HydrocolloidHydrocolloid
emulsifying agentsemulsifying agents
Accacia: (o/w)
Best E.A for oral emulsions, they have low viscocity,
so creaming occurs, addition of Tragacanth can
improve the stability.
Tragacanth
High viscocity, used as emulsions stabilizer
Agar
Extract from sea weed, used as emulsion stabilizer
Soluble in boiling water, on cooling it forms gel.
Low conc is used if the product is to be poured (oral)
33. 3333
Classification ofClassification of HydrocolloidHydrocolloid
emulsifying agentsemulsifying agents
Lecithin
They are used for formulating o/w emulsions. Purified
lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It forms w/o emulsion.
Wool fat
It is mainly used in w/o emulsions meant for external
use. It is also used as eye ointment base
34. 3434
Finely divided solidsFinely divided solids
• Description :
Finely divided solid particles that are wetted to some
degree by both oil and water act as emulsifying agents.
This results from their being concentrated at interface,
where they produce a particulate film around the
dispersed droplets to prevent coalescence.
36. 3636
Classification of Finely dividedClassification of Finely divided
solid emulsifying agentssolid emulsifying agents
• Bentonite
• Depend on the order of mixing, both o/w or
w/o emulsion can be formed with bentonite.
For o/w emulsion, bentonite is first
dispersed in water and allowed to hydrate to
form magma. Then oil phase is gradually
added with constant agitation. To prepare
w/o emulsion, bentonite is first dispersed in
oil and then water is added gradually.
37. 3737
Auxiliary emulsifying agentsAuxiliary emulsifying agents
• Auxiliary (Secondary) emulsifying agents include those
compounds that are normally incapable themselves of
forming stable emulsion. Their main value lies in their
ability to function as thickening agents and thereby help
stabilize the emulsion.
• E.g Stearic acid, Methyl cellulose
38. 3838
Selection of emulsifying agentSelection of emulsifying agent
Properties of an ideal emulsifying agent
reduce the interfacial tension between the
two immiscible liquids.
completely non irritant and non toxic in the
concentrations used.
produce and maintain the required
viscosity of the preparation.
39. 3939
Preservation of emulsionsPreservation of emulsions
• Microbial contamination may occur due to:
• contamination during development or production of emulsion or during its
use.
• Usage of impure raw materials
• Poor sanitation conditions
• Contamination by the consumer during use of the product..
• Precautions to prevent microbial growth ;
• Use of uncontaminated raw materials
• Careful cleaning of equipment.
• Addition of anti microbial agent
40. 4040
Antimicrobial agentsAntimicrobial agents
• The preservative must be :
• Less toxic
• Stable to heat and storage
• Chemically compatible
• Reasonable cost
• Acceptable taste, odor and color.
• Effective against fungus, yeast, bacteria.
• Preservative must no bind to other components of the
emulsion
44. 4444
Dry gum method ( ContinentalDry gum method ( Continental
method)method)
• used to prepare the initial or primary emulsion
from oil , water and a hydrocolloid or “gum” type
emulsifier ( usually acacia).
• Ratio of oil :gum : water in primary emulsion
Fixed oil = 4:1:2
Mineral oil = 3:1:2
Volatile oil = 2:1;2
45. 4545
Dry gum method ( ContinentalDry gum method ( Continental
method)method)
• In a mortar gum ( acacia) is levigated with oil until the
powder is thoroughly wetted; Then water is added all at
once and the mixture is vigorously and continuously
triturated until the primary emulsion formed is creamy
white.
• Additional water or aqueous solutions may be
incorporated after the primary emulsion is formed.
• Excipients ( e.g. active ingredients, preservatives , color,
flavors) are generally dissolved and added as a solution
to the primary emulsion ,
46. 4646
Dry gum method ( ContinentalDry gum method ( Continental
method)method)
• oil soluble substances in small amounts may be
incorporated directly into the primary emulsion.
• Any substance which might reduce the physical stability
of the emulsion, such as alcohol ( which may precipitate
the gum) should be added as near to the end of the
process as possible to avoid breaking the emulsion.
• When all agents have been incorporated , the emulsion
should be transferred to a calibrated vessel, brought to
final volume with water, then homogenized or blended to
ensure uniform distribution of ingredients.
47. 4747
Wet gum method (English method)Wet gum method (English method)
• The proportion of oil and water and emulsifier ( gum) are the same
as in dry gum method , but the order and technique of mixing are
different.
• The gum is triturated with water to form a mucilage;
• Then oil is slowly added in portions , while triturating.
• After all the oil is added , the mixture is triturated for several minutes
to form the primary emulsion.
• Then other ingredients are added as in continental method.
• Generally speaking, the English method is more difficult to perform
successfully , especially with more viscous oils, but may result in a
more stable emulsion.
48. 4848
Bottle methodBottle method
• Used to prepare emulsions of volatile oils, or oligeneous
substances of vary low viscosities.
• Acacia ( or other gum) is placed in a dry bottle and oil
are added,
• The bottle is capped and thoroughly shaken.
• To this the required volume of water is added all at once
and the mixture is shaken thoroughly until the primary
emulsion is formed.
•
49. 4949
Preparation of emulsionsPreparation of emulsions
Mechanical equipment for emulsification
(Agitation)
• Mechanical stirrers
• Propeller type mixers
-Turbine mixers
• Colloid mills
• Ultrasonifiers
52. 5252
Propeller stirrersPropeller stirrers
• Standard stirring
element. For drawing
the material to be mixed
from the top to the
bottom.
• Local shearing forces.
• Generates axial flow in
the vessel.
• Used at medium to high
speeds.
.
56. 5656
Physical instability of emulsionsPhysical instability of emulsions
• Physical instability
• i. Flocculation
• Ii. Creaming or sedimentation
• iii. coalescence
• Iv. Phase inversion
57. 5757
Physical instability of emulsionsPhysical instability of emulsions
Emulsion
Coalescence
Flocculation
Creaming
Breaking
58. 5858
Physical instability of emulsionsPhysical instability of emulsions
•Aggregation/flocculation : Dispersed particles
come together but do not fuse.
•Coalescence is the process by which emulsified
particles merge with each to form large particles.
•Breaking is the destroying of the film surrounding
the particles.
•Creaming & Sedimentation: upward or downward
movement or particles
59. 5959
Physical instability of emulsionsPhysical instability of emulsions
Flocculation :
• Redispersible association of particle within
an emulsion to form large aggregates.
• Precursor to the irreversible coalescence.
• differs from coalescence mainly in that
interfacial film and individual droplets remain
intact.
60. 6060
• Flocculation is influenced by the charges on
the surface of the emulsified globules.
• The reversibility of flocculation depends
upon strength of interaction between
particles as determined by
• chemical nature of emulsifier,
• phase volume ratio,
• concentration of dissolved substances,
specially electrolytes and ionic emulsifiers.
61. 6161
Physical instability of emulsionsPhysical instability of emulsions
Creaming & Sedimentation
• Creaming is the upward movement of dispersed
droplets of emulsion relative to the continuous
phase and Sedimentation is downward
movement of doplets ( due to the density
difference between two phases).
• Stoke’s law : dx / dt = d2 (ρi- ρe)g/18η
• Dx/dt = rate of setting
• D = diameter of particles
• ρi and ρe density of internal nd external phase
• g = gravitational constant
• η =viscosity of medium
62. Methods to reduceMethods to reduce
Creaming/SettlingCreaming/Settling
• Reduction in droplet size helps in
reducing creaming or sedimentation.
• increase in viscosity of the continuous
phase by adding thickening agents can
reduce the rate of creaming,
sedimentation, phase inversion
• Minimizing difference in densities of 2
phases (difficult to control) usually by 6262
63. 6363
Physical instability of emulsionsPhysical instability of emulsions
Coalescence and breaking
Coalescence is also called Cracking.
Irreversible process.
Sheath of EA around globules is lost.
It can lead to Breaking (Separation of two
phases)
64. 6464
Factors reducing the chance ofFactors reducing the chance of
Coalescence/breakingCoalescence/breaking
Uniformity in particle size (small size)
Increase in viscosity of dispersed phase
Maintain phase volume ratio
65. 6565
Physical instability of emulsionsPhysical instability of emulsions
Phase inversion
• An emulsion is said to invert when it
changes from an o/w to w/o or vice versa.
• Changing nature of emulsifying agent
• Alteration in phase volume ratio
• e.g o/w emulsifier is mixed with oil and
little quantity of water, it will form w/o
emulsion by agitation. But when more
water is added, it converts into o/w
emulsion.
TYPES OF EMULSIONS :
1. Macroemulsions (Simple Emulsions) :
i. Oil in water (o/w) : Oil droplets are dispersed in a continuous aqueous phase. This emulsion is generally formed if the aqueous phase constitutes more than 45 % of the total weight and a hydrophilic emulsifier is used. These are [referred for oral administration and cosmetics . These are useful as water washable drug bases .The globule size is 0.25 to 10 microns.
ii. Water in oil (w/o) : Aqueous droplets are dispersed in continuous oily phase. . This emulsion is generally formed if the oily phase constitutes more than 45 % of the total weight and a lipophobic emulsifier is used. These are used for cosmetics. The are employed for treatment of dry skin and emollient applications.
2. Multiple emulsions :
They are developed with a view to delay the release of an active ingredient. They have three phases. They may be oil-in-water-in-oil (o/w/o) or of water-in-oil-in-water (w/o/w). An emulsifier is present to stabilize the emulsions and various ionic and nonionic surfactants are available for this purpose. Lipophilic (oil-soluble, low HLB) surfactants are used to stabilize w/o emulsions, whereas hydrophilic (water-soluble, high HLB) surfactants are used to stabilize o/w systems In these emulsions within emulsions any drug present in innermost phase must now cross two phase boundaries to reach the external continuous phase.
Such emulsions also can invert. However, during inversion they form simple emulsions. So a w/o/w emulsion will get inverted to o/w emulsion.
Preparation of multiple emulsions :
Aqueous phase is added to oily phase, containing a lipophilic surfactant.Upon mixing a w/o emulsion is formed.
Ii. This w/o emulsuion is then poured into a second aqueous solution , containg za hydrophilic surfsactsnt. Upon mixing multiple emulsion w/o/w is formed.
Types of multiple emulsions : w/o/w , o/w/o
.Applications :
The important applications are in cosmetics ,pharmaceuticals and foods. For example, in cosmetics they have a fine texture and a smooth touch upon application, and they are aimed for slow and sustained release of active matter from an internal reservoir into the continuous phase (mostly water). They can serve as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. They can also improve dissolutions or solubilization of insoluble materials. Due to these properties, multiple emulsions find applications related to protecting sensitive and active molecules such as vitamins C and E from the external phase—a process called antioxidation
3. Microemulsions:
They may be defined as dispersions of insoluble liquids in a second liquid that appears clear and homogenous to the naked eye. They are frequently called solubilised systems because on a macroscopic basis they seem to behave as true solutions. Terms as transparent emulsions, micellar solutions, solubilised systems, swollen micelle have all been applied to the same or similar systems.
These emulsions appear to be transparent to the eye. They have globule radius below the range of 10-75 nm. The appearance of emulsion depends on the wavelength of visible light i.e. globules less than 120 nm do not reflect light and appear transparent to the eye. As in microemulsions the globule size is less than 120 nm, they appear to be transparent.
Blending of a small amount of oil and water results in a two phase system because “ water and oil do not mix “ If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic nature. This type of micellar microemulsion is also called an o/w micellar solution . Similarly , w/o solubilization – especially that by a nonionic surfactant – has been attributed to swollen micelles. In these systems , sometimes called reverse micelle solutions , water molecules are found in the polar central portion of a surfactant micelle., the non portion of which is in contact with the continuous lipid phase. A third type of microemulsion is formed by ionic surfactants (e.g.sodium stearate) in the presence of co-surfactant ) e.g. pentanol or dioxyethylene dodecyl ether) with hydrocarbons ( e.g. hexadecane ) and water.
In general microemulsions are believed to be thermodynamically stable. These microemulsions are used for drug administration and toiletry products.
TYPES OF EMULSIONS :
1. Macroemulsions (Simple Emulsions) :
i. Oil in water (o/w) : Oil droplets are dispersed in a continuous aqueous phase. This emulsion is generally formed if the aqueous phase constitutes more than 45 % of the total weight and a hydrophilic emulsifier is used. These are [referred for oral administration and cosmetics . These are useful as water washable drug bases .The globule size is 0.25 to 10 microns.
ii. Water in oil (w/o) : Aqueous droplets are dispersed in continuous oily phase. . This emulsion is generally formed if the oily phase constitutes more than 45 % of the total weight and a lipophobic emulsifier is used. These are used for cosmetics. The are employed for treatment of dry skin and emollient applications.
2. Multiple emulsions :
They are developed with a view to delay the release of an active ingredient. They have three phases. They may be oil-in-water-in-oil (o/w/o) or of water-in-oil-in-water (w/o/w). An emulsifier is present to stabilize the emulsions and various ionic and nonionic surfactants are available for this purpose. Lipophilic (oil-soluble, low HLB) surfactants are used to stabilize w/o emulsions, whereas hydrophilic (water-soluble, high HLB) surfactants are used to stabilize o/w systems In these emulsions within emulsions any drug present in innermost phase must now cross two phase boundaries to reach the external continuous phase.
Such emulsions also can invert. However, during inversion they form simple emulsions. So a w/o/w emulsion will get inverted to o/w emulsion.
Preparation of multiple emulsions :
Aqueous phase is added to oily phase, containing a lipophilic surfactant.Upon mixing a w/o emulsion is formed.
Ii. This w/o emulsuion is then poured into a second aqueous solution , containg za hydrophilic surfsactsnt. Upon mixing multiple emulsion w/o/w is formed.
Types of multiple emulsions : w/o/w , o/w/o
.Applications :
The important applications are in cosmetics ,pharmaceuticals and foods. For example, in cosmetics they have a fine texture and a smooth touch upon application, and they are aimed for slow and sustained release of active matter from an internal reservoir into the continuous phase (mostly water). They can serve as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. They can also improve dissolutions or solubilization of insoluble materials. Due to these properties, multiple emulsions find applications related to protecting sensitive and active molecules such as vitamins C and E from the external phase—a process called antioxidation
3. Microemulsions:
They may be defined as dispersions of insoluble liquids in a second liquid that appears clear and homogenous to the naked eye. They are frequently called solubilised systems because on a macroscopic basis they seem to behave as true solutions. Terms as transparent emulsions, micellar solutions, solubilised systems, swollen micelle have all been applied to the same or similar systems.
These emulsions appear to be transparent to the eye. They have globule radius below the range of 10-75 nm. The appearance of emulsion depends on the wavelength of visible light i.e. globules less than 120 nm do not reflect light and appear transparent to the eye. As in microemulsions the globule size is less than 120 nm, they appear to be transparent.
Blending of a small amount of oil and water results in a two phase system because “ water and oil do not mix “ If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic nature. This type of micellar microemulsion is also called an o/w micellar solution . Similarly , w/o solubilization – especially that by a nonionic surfactant – has been attributed to swollen micelles. In these systems , sometimes called reverse micelle solutions , water molecules are found in the polar central portion of a surfactant micelle., the non portion of which is in contact with the continuous lipid phase. A third type of microemulsion is formed by ionic surfactants (e.g.sodium stearate) in the presence of co-surfactant ) e.g. pentanol or dioxyethylene dodecyl ether) with hydrocarbons ( e.g. hexadecane ) and water.
In general microemulsions are believed to be thermodynamically stable. These microemulsions are used for drug administration and toiletry products.
TYPES OF EMULSIONS :
1. Macroemulsions (Simple Emulsions) :
i. Oil in water (o/w) : Oil droplets are dispersed in a continuous aqueous phase. This emulsion is generally formed if the aqueous phase constitutes more than 45 % of the total weight and a hydrophilic emulsifier is used. These are [referred for oral administration and cosmetics . These are useful as water washable drug bases .The globule size is 0.25 to 10 microns.
ii. Water in oil (w/o) : Aqueous droplets are dispersed in continuous oily phase. . This emulsion is generally formed if the oily phase constitutes more than 45 % of the total weight and a lipophobic emulsifier is used. These are used for cosmetics. The are employed for treatment of dry skin and emollient applications.
2. Multiple emulsions :
They are developed with a view to delay the release of an active ingredient. They have three phases. They may be oil-in-water-in-oil (o/w/o) or of water-in-oil-in-water (w/o/w). An emulsifier is present to stabilize the emulsions and various ionic and nonionic surfactants are available for this purpose. Lipophilic (oil-soluble, low HLB) surfactants are used to stabilize w/o emulsions, whereas hydrophilic (water-soluble, high HLB) surfactants are used to stabilize o/w systems In these emulsions within emulsions any drug present in innermost phase must now cross two phase boundaries to reach the external continuous phase.
Such emulsions also can invert. However, during inversion they form simple emulsions. So a w/o/w emulsion will get inverted to o/w emulsion.
Preparation of multiple emulsions :
Aqueous phase is added to oily phase, containing a lipophilic surfactant.Upon mixing a w/o emulsion is formed.
Ii. This w/o emulsuion is then poured into a second aqueous solution , containg za hydrophilic surfsactsnt. Upon mixing multiple emulsion w/o/w is formed.
Types of multiple emulsions : w/o/w , o/w/o
.Applications :
The important applications are in cosmetics ,pharmaceuticals and foods. For example, in cosmetics they have a fine texture and a smooth touch upon application, and they are aimed for slow and sustained release of active matter from an internal reservoir into the continuous phase (mostly water). They can serve as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. They can also improve dissolutions or solubilization of insoluble materials. Due to these properties, multiple emulsions find applications related to protecting sensitive and active molecules such as vitamins C and E from the external phase—a process called antioxidation
3. Microemulsions:
They may be defined as dispersions of insoluble liquids in a second liquid that appears clear and homogenous to the naked eye. They are frequently called solubilised systems because on a macroscopic basis they seem to behave as true solutions. Terms as transparent emulsions, micellar solutions, solubilised systems, swollen micelle have all been applied to the same or similar systems.
These emulsions appear to be transparent to the eye. They have globule radius below the range of 10-75 nm. The appearance of emulsion depends on the wavelength of visible light i.e. globules less than 120 nm do not reflect light and appear transparent to the eye. As in microemulsions the globule size is less than 120 nm, they appear to be transparent.
Blending of a small amount of oil and water results in a two phase system because “ water and oil do not mix “ If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic nature. This type of micellar microemulsion is also called an o/w micellar solution . Similarly , w/o solubilization – especially that by a nonionic surfactant – has been attributed to swollen micelles. In these systems , sometimes called reverse micelle solutions , water molecules are found in the polar central portion of a surfactant micelle., the non portion of which is in contact with the continuous lipid phase. A third type of microemulsion is formed by ionic surfactants (e.g.sodium stearate) in the presence of co-surfactant ) e.g. pentanol or dioxyethylene dodecyl ether) with hydrocarbons ( e.g. hexadecane ) and water.
In general microemulsions are believed to be thermodynamically stable. These microemulsions are used for drug administration and toiletry products.
TYPES OF EMULSIONS :
1. Macroemulsions (Simple Emulsions) :
i. Oil in water (o/w) : Oil droplets are dispersed in a continuous aqueous phase. This emulsion is generally formed if the aqueous phase constitutes more than 45 % of the total weight and a hydrophilic emulsifier is used. These are [referred for oral administration and cosmetics . These are useful as water washable drug bases .The globule size is 0.25 to 10 microns.
ii. Water in oil (w/o) : Aqueous droplets are dispersed in continuous oily phase. . This emulsion is generally formed if the oily phase constitutes more than 45 % of the total weight and a lipophobic emulsifier is used. These are used for cosmetics. The are employed for treatment of dry skin and emollient applications.
2. Multiple emulsions :
They are developed with a view to delay the release of an active ingredient. They have three phases. They may be oil-in-water-in-oil (o/w/o) or of water-in-oil-in-water (w/o/w). An emulsifier is present to stabilize the emulsions and various ionic and nonionic surfactants are available for this purpose. Lipophilic (oil-soluble, low HLB) surfactants are used to stabilize w/o emulsions, whereas hydrophilic (water-soluble, high HLB) surfactants are used to stabilize o/w systems In these emulsions within emulsions any drug present in innermost phase must now cross two phase boundaries to reach the external continuous phase.
Such emulsions also can invert. However, during inversion they form simple emulsions. So a w/o/w emulsion will get inverted to o/w emulsion.
Preparation of multiple emulsions :
Aqueous phase is added to oily phase, containing a lipophilic surfactant.Upon mixing a w/o emulsion is formed.
Ii. This w/o emulsuion is then poured into a second aqueous solution , containg za hydrophilic surfsactsnt. Upon mixing multiple emulsion w/o/w is formed.
Types of multiple emulsions : w/o/w , o/w/o
.Applications :
The important applications are in cosmetics ,pharmaceuticals and foods. For example, in cosmetics they have a fine texture and a smooth touch upon application, and they are aimed for slow and sustained release of active matter from an internal reservoir into the continuous phase (mostly water). They can serve as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. They can also improve dissolutions or solubilization of insoluble materials. Due to these properties, multiple emulsions find applications related to protecting sensitive and active molecules such as vitamins C and E from the external phase—a process called antioxidation
3. Microemulsions:
They may be defined as dispersions of insoluble liquids in a second liquid that appears clear and homogenous to the naked eye. They are frequently called solubilised systems because on a macroscopic basis they seem to behave as true solutions. Terms as transparent emulsions, micellar solutions, solubilised systems, swollen micelle have all been applied to the same or similar systems.
These emulsions appear to be transparent to the eye. They have globule radius below the range of 10-75 nm. The appearance of emulsion depends on the wavelength of visible light i.e. globules less than 120 nm do not reflect light and appear transparent to the eye. As in microemulsions the globule size is less than 120 nm, they appear to be transparent.
Blending of a small amount of oil and water results in a two phase system because “ water and oil do not mix “ If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic nature. This type of micellar microemulsion is also called an o/w micellar solution . Similarly , w/o solubilization – especially that by a nonionic surfactant – has been attributed to swollen micelles. In these systems , sometimes called reverse micelle solutions , water molecules are found in the polar central portion of a surfactant micelle., the non portion of which is in contact with the continuous lipid phase. A third type of microemulsion is formed by ionic surfactants (e.g.sodium stearate) in the presence of co-surfactant ) e.g. pentanol or dioxyethylene dodecyl ether) with hydrocarbons ( e.g. hexadecane ) and water.
In general microemulsions are believed to be thermodynamically stable. These microemulsions are used for drug administration and toiletry products.
TYPES OF EMULSIONS :
1. Macroemulsions (Simple Emulsions) :
i. Oil in water (o/w) : Oil droplets are dispersed in a continuous aqueous phase. This emulsion is generally formed if the aqueous phase constitutes more than 45 % of the total weight and a hydrophilic emulsifier is used. These are [referred for oral administration and cosmetics . These are useful as water washable drug bases .The globule size is 0.25 to 10 microns.
ii. Water in oil (w/o) : Aqueous droplets are dispersed in continuous oily phase. . This emulsion is generally formed if the oily phase constitutes more than 45 % of the total weight and a lipophobic emulsifier is used. These are used for cosmetics. The are employed for treatment of dry skin and emollient applications.
2. Multiple emulsions :
They are developed with a view to delay the release of an active ingredient. They have three phases. They may be oil-in-water-in-oil (o/w/o) or of water-in-oil-in-water (w/o/w). An emulsifier is present to stabilize the emulsions and various ionic and nonionic surfactants are available for this purpose. Lipophilic (oil-soluble, low HLB) surfactants are used to stabilize w/o emulsions, whereas hydrophilic (water-soluble, high HLB) surfactants are used to stabilize o/w systems In these emulsions within emulsions any drug present in innermost phase must now cross two phase boundaries to reach the external continuous phase.
Such emulsions also can invert. However, during inversion they form simple emulsions. So a w/o/w emulsion will get inverted to o/w emulsion.
Preparation of multiple emulsions :
Aqueous phase is added to oily phase, containing a lipophilic surfactant.Upon mixing a w/o emulsion is formed.
Ii. This w/o emulsuion is then poured into a second aqueous solution , containg za hydrophilic surfsactsnt. Upon mixing multiple emulsion w/o/w is formed.
Types of multiple emulsions : w/o/w , o/w/o
.Applications :
The important applications are in cosmetics ,pharmaceuticals and foods. For example, in cosmetics they have a fine texture and a smooth touch upon application, and they are aimed for slow and sustained release of active matter from an internal reservoir into the continuous phase (mostly water). They can serve as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. They can also improve dissolutions or solubilization of insoluble materials. Due to these properties, multiple emulsions find applications related to protecting sensitive and active molecules such as vitamins C and E from the external phase—a process called antioxidation
3. Microemulsions:
They may be defined as dispersions of insoluble liquids in a second liquid that appears clear and homogenous to the naked eye. They are frequently called solubilised systems because on a macroscopic basis they seem to behave as true solutions. Terms as transparent emulsions, micellar solutions, solubilised systems, swollen micelle have all been applied to the same or similar systems.
These emulsions appear to be transparent to the eye. They have globule radius below the range of 10-75 nm. The appearance of emulsion depends on the wavelength of visible light i.e. globules less than 120 nm do not reflect light and appear transparent to the eye. As in microemulsions the globule size is less than 120 nm, they appear to be transparent.
Blending of a small amount of oil and water results in a two phase system because “ water and oil do not mix “ If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic nature. This type of micellar microemulsion is also called an o/w micellar solution . Similarly , w/o solubilization – especially that by a nonionic surfactant – has been attributed to swollen micelles. In these systems , sometimes called reverse micelle solutions , water molecules are found in the polar central portion of a surfactant micelle., the non portion of which is in contact with the continuous lipid phase. A third type of microemulsion is formed by ionic surfactants (e.g.sodium stearate) in the presence of co-surfactant ) e.g. pentanol or dioxyethylene dodecyl ether) with hydrocarbons ( e.g. hexadecane ) and water.
In general microemulsions are believed to be thermodynamically stable. These microemulsions are used for drug administration and toiletry products.
Microemulsions:
They may be defined as dispersions of insoluble liquids in a second liquid that appears clear and homogenous to the naked eye. They are frequently called solubilised systems because on a macroscopic basis they seem to behave as true solutions. Terms as transparent emulsions, micellar solutions, solubilised systems, swollen micelle have all been applied to the same or similar systems.
These emulsions appear to be transparent to the eye. They have globule radius below the range of 10-75 nm. The appearance of emulsion depends on the wavelength of visible light i.e. globules less than 120 nm do not reflect light and appear transparent to the eye. As in microemulsions the globule size is less than 120 nm, they appear to be transparent.
Blending of a small amount of oil and water results in a two phase system because “ water and oil do not mix “ If the same small amount of oil is added to an aqueous solution of a suitable surfactant in the micellar state, the oil may preferentially dissolve in the interior of the micelle because of its hydrophobic nature. This type of micellar microemulsion is also called an o/w micellar solution . Similarly , w/o solubilization – especially that by a nonionic surfactant – has been attributed to swollen micelles. In these systems , sometimes called reverse micelle solutions , water molecules are found in the polar central portion of a surfactant micelle., the non portion of which is in contact with the continuous lipid phase. A third type of microemulsion is formed by ionic surfactants (e.g.sodium stearate) in the presence of co-surfactant ) e.g. pentanol or dioxyethylene dodecyl ether) with hydrocarbons ( e.g. hexadecane ) and water.
In general microemulsions are believed to be thermodynamically stable. These microemulsions are used for drug administration and toiletry products.
Thermodynamic - the energies involved.
Factors affecting the type of emulsion:
Type of emulsion produced (o/w or w/o) depends upon following factors :
Type of emulsifying agent :
Type of emulsion is a function of relative solubility of emulsifying agent . The phase in which it is soluble becomes the continuous phase.
The phase volume ratio i.e. the relative amount of oil and water.
This determines the relative number of droplets formed and hence the probability of number of collision. The greater the number of droplets, greater is the chance for collision. Thus the phase present in greater amount becomes the external phase.
The polar portions of the emulsifying agents are better barriers to coalescence than hydrocarbon counterparts. So o/w emulsions can be formed with relatively high internal phase volume. In w/o emulsion ( in which the barrier is of hydrocarbon nature) if the amount of internal phase is increased more than 40 % , it inverts to o/w emulsion because hydrocarbon part of surfactant can not form a strong barrier.
Viscosity of each phase :
An increase in viscosity of a phase helps in making that phase the external phase.
USES( APPLICATIONS) OF EMULSIONS :
Emulsions can be used for oral , parenteral or topical pharmaceutical dosage forms.
i. Oral Products
Emulsions are used for administering drugs orally due to following reasons :
a. More palatable : Objectionable taste or texture of medicinal agents gets masked.
b. Better absorption : Due to small globule size, the medicinal agent gets absorbed faster.
ii. Topical products :
o/w emulsions are more acceptable as water washable drug bases for cosmetic purposes.
w/o emulsions are used for treatment of dry skin. Emulsions have following advanyages when used for topical purpose:
a. Patient acceptance : Emulsions are accepted by patients due to their elegance, easily
b. washable character,
c. acceptable viscosity,
d. less greasiness.
iii. Parenteral Emulsions :
a. i.v rout :
Lipid nutrients are emulsified and given to patients by i/v rout. Such emulsions have particle size less than 100 nm.
b. Depot injections :
W/o emulsions are used to disperse water soluble antigenic materials in mineral oil for i/m depot injection.
Diagnostic purposes :
Radio opaque emulsions have been used in X-ray examination.
Emulsifying agents
They are the substances added to an emulsion to prevent the coalescence of the globules of the dispersed phase. They are also known as emulgents or emulsifiers.
They help in formation of emulsion by three mechanisms.
Reduction in interfacial tension – thermodynamic stabilization
Formation of a rigid interfacial film – mechanical barrier to coalescence
Formation of an electrical double layer – electrical barrier to approach of particles.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Classification of emulsifying agents
Synthetic emulsifying agents (Surfactants):
This group contains surface active agents which act by getting adsorbed at the oil water interface in such a way that the hydrophilic polar groups are oriented towards water and lipophillic non polar groups are oriented towards oil, thus forming a stable film. This film acts as a mechanical barrier and prevents coalescence of the globules of the dispersed phase. They are classified according to the ionic charge possessed by the molecules of the surfactant e.g., anionic, cationic, non-ionic and ampholytic.
: They may be subdivided into anionic, cationic and nonionic surfactants.
i. Anionic Surfactants : The long anion chain on dissociation imparts surface activity, while the cation is inactive. These agents are primarily used for external preparations and not for internal use as they have an unpleasant bitter taste and irritant action on the intestinal mucosa. e.g., alkali soaps, polyvalent soaps (metallic soaps), organic soaps, sulphated alcohols and alkyl sulphonates.
a. Monovalent soaps : E.g. potassium, sodium, ammonium salts of lauric and oleic acid . They are soluble in water and are good o/w emulsifying agents.
Disadvantages :
They have disagreeable taste and are irritating to the GIT.. So they are useful only for external use emulsions.
They have a high pH . They get ppted below pH 10 because the unionized fatty acid is formed which has a low aqueous solubility. So emulsions formed with alkali soaps are not stable at pH less than 10.
b. Polyvalent soaps : The calcium, magnesium and aluminum salts of fatty acids ( metallic soaps) are water insoluble and give w/o emulsion.
c. Organic soaps : Triethanol amine soaps of fatty acids give o/w emulsion. They are used for external use emulsions. They are less alkaline as compare to monovalent soaps . They can act till pH 8.00
d. Sulfated alcohols : They are neutralized estrs of sulfuric acid and fatty alcohols. They can be used as auxiliary emulsifying agents. E.g Sodium lauryl sulphate
e. Sulfonates : In these compounds the sulfur atom is connected directly to the carbon atom, giving the general formula
CH3(CH2)n CH2SO3 – Na+
e.g. sodium lauryl sulphate , dioctyl sulphosuccinate.
ii. Cationic Surfactants: The positive charge cations produced on dissociation are responsible for emulsifying properties. They are mainly used in external preparations such as lotions and creams. Quaternary ammonium compounds such as cetrimide, benzalkonium chloride and benzethonium chloride are examples of important cationic surfactants. These compounds besides having good antibacterial activity are also used in combination with secondary emulsifying agents to produce o/w emulsions for external application.
Quaternary ammonium compounds (cetyl trimethyl ammonium bromide ; cetrimide)
CH3(CH2)14 N+ (CH3)34Br
They have marked bactericidal activity. activity. So they are useful for anti infective products such as skin lotions and creams. The pH of an emulsion prepared with cationic emulsifier is in pH 4 -6 range. This is the range of normal pH of skin. So They are suitable for skin. They are comparatively weak emulsifying agents, so they are used along with auxiliary emulsifying agents such as cetostearyl alcohol. They are incompatible with anionic surfactants.
Nonionics :
They are the class of surfactants widely used as emulsifying agents. They are extensively used to produce both oil in water and water in oil emulsions for internal as well as external use.
Advantages : They are not susceptible to pH change and presence of electrolytes.
They also show low irritancy as compared to other surfactants.
Most commonly used nonionics are
glyceryl esters ,
polyoxyethylene glycol esters and ethers
sorbitan fatty acid esters (spans)
polyoxyethylene derivatives of sorbitan fatty acid esters (Tweens or polysorbates)
Polyoxyethylene / polyoxypropylene block polymers (Poloxamers)
Glyceryl esters : e.g. glyceryl mono stearate. It is too lipophilic to be used as a primary emulsifying agent. It is used as auxiliary emulsifying agent.
. CH2OOC C17H35
CHOH
CH2OH
Sorbitan fatty acid esters : e.g. sorbitan mono oleate. They are oil soluble nonionic surfactants.and give w/o emulsions.
HO OH
O CH(OH) CH2-OOC-R
Polyoxyethylene derivatives of sorbitans fatty acids : They are hydrophilic and give o/w emulsion.
OH(C2H4O)n (OCH2)nOH
CH2-OOC-R
O CH(O CH2)nOH
Polyoxyethylene/polyoxypropylene block poymers , also known as poloxamers consist of combined chains of oxyethylene with oxypropylene where the oxyethylene portions imparts hydrophilicity and oxypropylene portion imparts lipophilicity. The molecules are synthesized as long segments of hydrophilic portions combined with long segments of the hydrophilic portions, with each portion referred to as block. They are used in the formulation of i/v emulsions and can impart structures to vehicles and interfacial films.
). iv) Ampholytic surfactants: These are the substances whose ionic charge depends on the pH of the system. Below a certain pH, these are cationic while above a defined pH, these are cationic. At intermediate pH these behave as zwitterions. e.g. lecithin.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
2. Semi-synthetic polysaccharides
Includes mainly cellulose derivatives like sodium carboxy methyl cellulose, hydroxyl propyl cellulose and methyl cellulose. They are used for formulating o/w type of emulsions. They primarily act by increasing the viscosity of the system. e.g., methyl cellulose, hydroxypropyl cellulose and sodium carboxy methyl cellulose
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
3. Natural emulsifying agents. :
i. Natural emulsifying agents from vegetable sources
These consist of agents which are carbohydrates and include gums and mucilaginous substances. Since these substances are of variable chemical composition, these exhibit considerable variation in emulsifying properties. They are anionic in nature and produce o/w emulsions. They act as primary emulsifying agents as well as secondary emulsifying agents (emulsion stabilizers). Since carbohydrates acts a good medium for the growth of microorganism, therefore emulsions prepared using these emulsifying agents have to be suitable preserved in order to prevent microbial contamination. E.g. tragacanth, acacia, agar, chondrus (Irish Moss), pectin and starch.
Acacia : It is a carbohydrate gum which is soluble over a wide pH range. It can be used as emulsifying agent in the following ratio to prepare primary emulsions :
Type of oilRatio of oil : gum : water for primary emulsionFixed oil 4 : 1: 2Mineral oil3 : 1 : 2Volatile oil2 : 1 ; 2Oleo gum resin1 : 1 : 2
Tragacanth, pectin and starch are used as auxiliary emulsifying agents.
ii. Natural emulsifying agents from animal source
The examples include gelatin, egg yolk and wool fat (anhydrous lanolin).
Gelatin :
It is a protein .It has two isoelectric points, depending on the method of preparation. Type a gelatin derived from acid treated precursor , has an isoelectric point between pH 7 and 9. Type B gelatin obtained from an alkaline precursor has an isoelectric point around pH 5. . Type A gelatin acts best as an emulsifier around pH 3 where it is -vely chaged: On the other hand type B gelatin suitable as emulsifier at pH 8 where it is –vely charged.
Type A gelatin (Cationic) is generally used for preparing o/w emulsion while type B gelatin is used for o/w emulsions of pH 8 and above.
Lecithin :
It is an emulsifier obtained from both plant (soyabean) and animal ( e.g. egg yolk) sources and is composed of phosphatides. Although the primary component of most lecithins is phosphatidyl choline . but it also contains phosphatidyl srine, phosphatidyl inositol, phosphatdylethanloamine and phosphatidic acid.. It imparts a net –ve charge to dispersed particles. They show surface activity and are used for formulating o/w emulsions. Lecithins are good emulsifying agents for naturally occurring oils such as soy, corn, or safflower. Purified lecithin from soy or egg yolk is used for i/v emulsions.
cholesterol :
It is a major constituent of wool alcohols , obtained by the saponification and fractionation of wool fat. It forms w/o emulsion. It is because of cholesterol that wool fat absorbs water and form a w/o emulsion It is also present in egg yolk.
Wool fat
It is mainly used in w/o emulsions meant for external use. They absorb large quantities of water and form stable w/o emulsions with other oils and fats.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Finely dispersed solids :
They form particulate films around the dispersed droplets, producing emulsions which are coarse grained but stable. Colloidal clays like bentonite, veegum are the examples of finely divided solids used as emulsifying agents.
Bentonite : It is a gray, odorless and tasteless powder which swells in the presence of water to form a suspension with a pH of about 9. Depend on the order of mixing, both o/w or w/o emulsion can be formed with bentonite. For o/w emulsion, bentonite is first dispersed in water and allowed to hydrate to form magma. Then oil phase is gradually added with constant agitation. To prepare w/o emulsion, bentonite is first dispersed in oil and then water is added gradually.
Veegum : Used as stabilizer in concentration of 1% for cosmetic lotions and creams. Prepared with anionic or non ionic emulsifying agents.
Auxiliary emulsifying agents :
These are those compounds which normally can not form an emulsion on their own but can function as thickening agents and stabilize the emulsion. Sometimes they increase the viscosity of the external phase and help restricting the collisions of droplets.. Some of them prevent coalescence by reducing van de waals forces between particles or by providing a physical barrier between droplets. Proteins, semisynthetic polysaccharides ( methyl cellulose, carboxy mthyl cellulose), clays can be used as auxiliary agents.
Selection of emulsifying agent :
Criteria For The Selection Of Emulsifying Agents
An ideal emulsifying agent should posses the following characteristics:
Choice of emulsifying agent
Choice of emulsifying agent depends upon
i. Shelf life of the product
ii. Type of emulsion desired
Cost of emulsifier.
Compatibility
Non toxicity
Taste
Chemical stability.
An emulsifying agent suitable for a skin cream may not be acceptable for oral preparation or i/v preparation due to its toxicity
HLB method for section of emulsifying agent :
The selection of surfactant to be used as emulsifying agent can be done by Griffin’s method. It is based on balance between hydrophilic and lipophilic portion of the emulsifying agent .
Griffin developed the system of Hydrophilic liophilic balance (HLB) of surfactants. The HLB value of the emulsifier can be found from the literature or determined experimentally or can be computed if the structural formula of the surfactant is known. It is defined as the mol % of hydrophilic group divded by 5. A completely hydrophilic molecule (without any non polar group has an HLB value of 20. The molecules that are water soluble have high HLB value; those which are oil soluble have low HLB value. Each surfactant is given a value between 0-18 It is used in the rational selection of combination of nonionic emulsifiers. If an o/w emulsion is required, formulator should choose an emulsifier with an HLB value in the range of 8-18. Emulsifier in the range of 4-6 can be used for w/o emulsions. Griffin also evolved a series of “required HLB values” by a particular material if it is to be emulsified in the form of o/w or w/o emulsion. The required HLB values for a particular oil will differ depending upon whether o/w or w/o emulsion is required.
Fundamental to the utility of the HLB value concept is the fact that the HLB values are algebraically additive. Thus calculations can be done to find the correct ratio of combination of low HLB value and high HLB value surfactant for a particular oil for a particular type of emulsion.
Example :
Liquid paraffin ( Required HLB 10.5) 15 gms
Emulsifying agents : 5 gms
(A) Sorbitan monooleate ( HLB 4.3)
(B) Polyoxyethylene 20 sorbitan mono oleate ( HLB 15.0)
Water
By allegation method , it can be found that (A) and (B) should be mixed in the ratio of 4.5 and 6.2 to get the required 10.5 HLB value. Because the formula calls for 5 gm of emulsifying agent , the required weights are 2.1 and 2.9 gms. Respectively.
The formulator can chose a single emulsifying agent which can yield HLB value of 10.5. But more often in case of o/w emulsions, stable emulsion can be produced by utilsing a combination of a hydrophilic and hydrophobic surfactant. Such combination appears to produce mixed interfacial phases of high surface coverage as well as of sufficient viscosity to prevent creaming and promote stability. HLB values of combination may be determined by taking weighted average of the individual surfactant HLB values. Many combinations can be tried to choose the best emulsifying agent.
If the HLB value of oil is not known, it becomes necessary to determine the parameter. Various blends are prepared to give a wide range of HLB mixture and emulsions are prepared in a standard manner. The HLB of the blend used to give the best product is taken to be the HLB of oil.
Microbial contamination may occur due to:
contamination during development or production of emulsion or during its use.
Usage of impure raw materials
Poor sanitation conditions
Invasion by an opportunistic microorganisms.
Contamination by the consumer during use of the product..
Precautions to prevent microbial growth ;
Use of uncontaminated raw materials
Careful cleaning of equipment with live straem .
Antimicrobial agents :
Emulsions often contain a number of ingredients such as carbohydrates, proteins, sterols and phosphatides., all of which readily support the growth of a varity of microorganisms. Even in the absence of any of the above mentioned ingredients, the mere presence of a mixture of lipid and water in intimate contact frequently allows microorganisms growth. So preservative is a must for emulsions.
Microbial contamination may occur due to:
contamination during development or production of emulsion or during its use.
Usage of impure raw materials
Poor sanitation conditions
Invasion by an opportunistic microorganisms.
Contamination by the consumer during use of the product..
Precautions to prevent microbial growth ;
Use of uncontaminated raw materials
Careful cleaning of equipment with live straem .
Preservation :
Once a microbiologically uncontaminated product has been formed, a relatively mild antimicrobial agent is sufficient to protect the product against microbial contamination. The preservative system must be effective against invasion by a variety of pathogenic organisms and protect the product during use by consumer.
The preservative must be :
Less toxic
Stable to heat and storage
Chemically compatible
Reasonable cost
Acceptable taste, odor and color.
Effective against fungus, yeast, bacteria.
Available in oil and aqueous phase at effective level concentration.
LABORATORY SCALE TECHNIQUES (EXTEMPORANEOUS METHOD OF PREPARATION OF EMULSIONS} ::
Emulsification process can be carried out by four methods :
Addition of internal phase to the external phase , while subjecting the system to shear or fracture.
Phase inversion technique: The external phase is added to the internal phase. E.g. if o/w emulsion is to be prepared, the aqueous phase is added to the oily phase. . First w/o emulsion is formed. At the inversion point the addition of more water results in the inversion of the emulsion system and formation of an o/w emulsion. This phase inversion technique allows the formation of small droplets with minimal mechanical action and heat. A classical example is the dry gum method
Mixing both phases after warming each : This methodic used for creams and ointments.
Alternate addition of two phases to the emulsifying agent : In this method, the water and oil are added alternatively , in small portions to the emulsifier . This technique is suitable for food emulsions.
Techniques used on laboratory scale
Continental or dry gum method
Wet gum method
Bottle or Forbes bottle method
Auxiliary method
In situ soap method
Dry gum method (Continental method)
The continental method is used to prepare the initial or primary emulsion from oil , water and a hydrocolloid or “gum” type emulsifier ( usually acacia). The primary emulsion or emulsion nucleus is formed from 4 parts of oil, 2 parts of water and one part of gum. The 4 parts of oil and 1 part of gum represent their total amount for the final emulsion.
In a mortar the 1 part of gum (acacia) is levigate with 4 parts of oil until the powder is thoroughly wetted; then the 2 parts water is added all at once and the mixture is vigorously and continuously triturated until the primary emulsion formed is creamy white.
Additional water or aqueous solutions may be incorporated after the primary emulsion is formed. Slid substances ( e.g. active ingredients, preservatives , color, flavors) are generally dissolved and added as a solution to the primary emulsion ,oil soluble substances in small amounts may be incorporated directly into the primary emulsion. Any substance which might reduce the physical stability of the emulsion, such as alcohol ( which may precipitate the gum) should be added as near to the end of the process as possible to avoid breaking the emulsion. When all agents have been incorporated , the emulsion should be transferred to a calibrated vessel, brought to final volume with water, then homogenized or blended to ensure uniform distribution of ingredients.
Example
Cod liver oil 50 ml
Acacia 12.5 gm
Syrup 10 ml
Flavor oil 0.4 ml
Purified oil up to 100 ml
1. Accurately weigh or measure each ingredient
Place cod liver oil in dry mortar
Add acacia and give it a very quick mix.
Add 25 ml of water and immediately triyturate to form thick white , homgenous primary emulsion.
Add flavor and mix.
Add syrup and mix.
Add sufficient water to total 100 ml.
Wet gum method :
In this method the proportion of oil and water and emulsifier ( gum) are the same ( 4:2:1) , but the order and technique of mixing are different. The 1 part of gum is triturated with 2 parts of water to form a mucilage; then 4 parts of oil is slowly added in portions , while triturating. After all the oil is added , the mixture is triturated for several minutes to form the primary emulsion. Then other ingredients are added as in continental method. Generally speaking, the English method is more difficult to perform successfully , especially with more viscous oils, but may result in a more stable emulsion.
Bottle method :
This method may be used to prepare emulsions of volatile oils, or oligeneous substances of vary low viscosities. This method is a variation of dry gum method. One part of powdered acacia ( or other gum) is placed in a dry bottle and 4 parts of oil are added, The bottle is capped and thoroughly shaken. To this the required volume of water is added all at once and the mixture is shaken thoroughly until the primary emulsion is formed. It is important to minimize the initial amount of time the gum and oil are mixed. The gum will tend to imbibe the oil and will become water proof.
Auxiliary method :
An emulsion prepared by other methods can also be improved by passing it through a hand homogenizer, which forces the emulsion through a very small orifice, reducing the dispersed droplet size toabout5 microns or less
In sito soap method :
Calcium Soaps : w/o emulsions contain oils such as oleic acid , in combination with lime water ( calcium hydroxide solution, USP). Prepared by mixing equal volumes of oil and lime water
Example :
Nascent soap : Oil Phase : Olive oil / oleic acid ; olive oil may be replaces by other oils but oleic acid must be added.
Lime water : Ca(OH)2 should be freshly prepared.
The emulsion formed is w/o
Method of preparation : Bottle method
Mortar method : When the formulation contains solid insoluble such as zinc oxide and calamine.
Low energy emulsification :
The emulsification by change in temp. requires considerable expenditure of energy during both heating and cooling cycles of emulsion formation. In low energy emulsification, all of the internal phase, but only a portion of the external phase is heated. After emulsification of the heated portions , the remainder of the external phase is added to the emulsion concentrate, or the preformed concentrate is blended into the continuous phase. In those emulsions in which a phase inversion temp. exists, the emulsion concentrate is preferably prepared above PIT which results in emulsion having extremely small droplets size. Good emulsions can be prepared by this method careful control of variables like emulsification temp. mixing time, mixing intensity, amount of external phase employed during emulsification and the method of blending
Mechanical equipment for emulsification ( Agitation)
Some sort of Agitation is needed to break internal phase into droplets. To break up the internal phase into droplets the liquid jet at high speed through a small diameter nozzle may be introduced into a second liquid or liquid may flow into a second liquid which is being agitated vigorously.
Once he initial break up into droplets gas occurred , the droplets continue to be subjected to additional forces due to turbulence , which causes further breakdown into smaller droplets.
The amount work depends on the length of time during which energy is supplied; thus timing becomes another physical parameter.
Timing :
During the initial period of agitation required for emulsification, droplets are formed. However as agitation continues, the chance for collision between droplets becomes more frequent and coalescence occurs. It is advisable, therefore to avoid excessive period of agitation during and after the formation of emulsion. The optimum time of agitation has to be determined empirically.
The best way of forming emulsion by shaking is to use intermittent shaking. The reason for time dependent droplet stabilization may be distribution of the emulsifier between the phases, slow formation of the film on the surface of the droplets or interruption of droplet formation by continuous shaking.
Timing also affects the speed with which the two immiscible liquids are blended. In the case of o/w emulsions , the rate at which the oil phase is added to the aqueous phase can affect the particle size and hence the stability of emulsion.
There is also a relationship between temp. and timing i.e. the cooling / heating cycle . It is common to prepare emulsions at high temp. . The coolong rate of the initially formed emulsion also has a profound influence on the ultimate characteristics of the emulsion.
Various types of equipment are available to bring about droplet break up and emulsification. either in laboratory or in production. Such equipment can be divided into four categories :
Mechanical stirrers, 2. Homogenizes 3. Ultrasonifiers 4. Colloid mills
The most important factor involved in the preparation of emulsion is the degree of shear and turbulence required to produce a given dispersion of liquid droplets. The amount of agitation required depends on total volume the liquid to be mixed , the viscosity of the system, and the interfacial tension at the oil water interface.
Mechanical stirrers :
An emulsion may be stirred by means of various impellers mounted on shafts, which are placed directly into the system to be emulsified. Impellers may be of following types :
Propeller type mixers : Simple top entering propeller mixers are adequate for routine development work in the laboratory and production if the viscosity of the
The degree of agitation is controlled by propeller rotation but the pattern of liquid flow and resultant efficiency of mixing are controlled by the type of impeller, its position in the container, the presence of baffles, and the general shape of the container.These stirrers can not be used when :
vigorous agitation is needed,
extremely small droplets are needed.
Foaming at high shear rates must be avoided.
These mixers may have paddle blades, counter rotating blades or planetary blades .
Turbine type mixers : If more vigorous agitation is required or viscosity is more , turbine type mixers can be used.
.
Homogenizers : :
In homogenizers the dispersion of two liquids is achieved by forcing their mixture through a small inlet orifice at big pressures.
A homogenizer consists of a pump that raises the pressure of the dispersion to a range of 500 to 5000 psi and an orifice through which the fluid impinges upon the hogenising valve held in place on the valve seat by a strong spring. As the pressure builds up, the spring is compressed and some of the dispersion escapes between the valve and valve seat. At this point , the energy that has been stored in the liquid as pressure is released instantaneously, and subjects the product to intense turbulence and hydraulic shear.
Homogenizers can be made with more than one emulsifying stage, and it is possible to recycle the emulsion through the homogenizer more than one time.
Homogenizers raise the temp. of the emulsion, hence cooling may be required.
It can be used when a reasonably monodisperse emulsion of small droplet size ( 1 nm) is required.
Colloid mills :
They operate on principle of high shear which is normally generated between rotar and stator of the mill. Colloid mill consists of a fixed stator plate and a high speed rotating rotator plae.Material drawn or pumped through an adjustable gap set between the rotor and stator is homgenised by the physical actin and he centrifugal force is created by high rotatoion of the rotor whcig operates within 0.005 to0.010 inch of the stator.
Ultrasonifiers :
Ultrasonic energy s used to produce pharmaceutical emulsions.
These transduced piezoelectric devices have limited output and are expensive.
They are useful for laboratory preparation of emulsions of moderate viscosity and extremely low particle size.
Commercial equipment is based n principle of Pohlmn liquid whistle. The dispersion is forced through an orifice at modest pressure and is allowed to impinge on a blade. The pressure range is from 150-350 psi . This pressure causes blade to vibrate rapidly to produce an ultrasonic note. When the system reaches a steady state, a cavitational field is generated at the leading edge of the blade and the pressure fluctuations of approx 60 tonnes psi can be achieved in commercial equipment.
Chemical parameters : ( Selection of ingredients for emulsions, Formualtion of emulsions) ( Discussed earlier)
EXAMPLE : ORAL EMULSION
A. Cotton seed oil ( 460 gms)
Sulfadiazine 200 gms
Sorbitan monostearate 84 gms.
B. Poly oxyethylene (20) sorbitan monostearate 36 gms
Sodium benzoate 2.0 gms
Sweetener q.s
Water 1000gms
C. Flavor oil q.s.
Procedure :
heat (A) to 50 o C and pass through colloidal mill
Add (A) at 50 o c to (B) at 65 o (C) and stir while colloning to 45o (C)
Add ( C ) and continue to stir until room temp. is reached.
Discussion :
Viscosity of the final product must be high in order to keep sulphadiazine in suspension . (Sulfadiazine is water insoluble compound.) This could be achieved by increasing the internal phase.
Internal phase : As the product is meant for oral use, Cotton seed oil is used as internal phase to prepare o/w emulsion.
Type of emulsion : O/w emulsion is preferred as it has better taste.
Emulsifying agent :
HLB of 10 is needed to prepare o/w cotton seed oil emulsion. A combination of two emulsifying agent ( sorbitan monostearate and polyoxythylene (20) sorbitan mono stearate is used to get a net value of HLB 10 . Combination is preferred as it gives a better interfacial film around globules.
Ratio required to get required HLB of 10 = a x 4.7 +b x 14.9 ,
a and b are the weight fractions of each of the two emulsifiers.
a + b = 1.
iv. Procedure :
The blend of oil, drug and lipophilic emulsifier is warmed and passed through a colloidal mill to reduce the particle size of sulphadiazine.
The emulsion is formed by adding the drug suspension to the aqueous phase Mixing of two phases is done at low temperature in order to avoid settling of sulphadiazine. Heating the drug suspension to 65 o C reduces the viscosity and causes excessive settling of drug particles .
Additon of flavouring oil at low temp. prevents its loss by volatility
EMULSION STABILITY ( INSTABILITY)
Physical stability :
The term emulsion stability refers to the ability of an emulsion to resist changes in the properties over time. , the more stable the emulsion, the more slowly its properties change .
Stability ( Instability) of the emulsion is related to four major phenomenon :
Flocculation
Creaming or sedimentation
Aggregation or coalescence
Phase inversion
Flocculation :
Flocculation is defined as the association of particle within an emulsion to form large aggregates. However these aggregates can easily be redispersed upon shaking. It is considered as a precursor to the irreversible coalescence. It differs from coalescence mainly in that interfacial film and individual droplets remain intact. Flocculation is influenced by the charges on the surface of the emulsified globules. The reversibility of flocculation depends upon strength of interaction between particles as determined by
a the chemical nature of emulsifier,
b the phase volume ratio,
c. the concentration of dissolved substances, specially electrolytes and ionic emulsifiers.
ii. Creaming and sedimentation :
The upward or down ward movement of dispersed droplets is termed creaming or sedimentation respectively. In any emulsion, creaming or sedimentation takes place depending on the densities of disperse and continuous phases. Creaming or sedimentation is undesirable as it may lead to coalescence.
Factors affecting rate of creaming :
Rate of creaming is governed by Stoke’s law. As per Stoke’s law
=2r 2(ρ1 - ρ2 ) g / 9η
υ = rate of creaming or sedimentation
r = radius of droplets of dispersed phase
ρ1 , ρ2 = density of dispersed and continuous phase respectively
g = gravitational rate constant
η = viscosity of continuous phase.
Droplet size :
As per Stoke’s law, rate of creaming is directly proportional to the square of radius or diameter of the droplet size. Smaller is the diameter of the droplet, lesser will be the rate of creaming. So reduction in droplet size helps in reducing creaming or sedimentation.
Difference in densities of dispersed and continuous phase :
As per Stoke’s law no creaming is possible if densities of the two phases are equal. So Creaming can be avoided by adjusting the density of dispersed phase.
Viscosity of the continuous phase :
As per Stoke’s law, rate of creaming is inversely proportional to viscosity of the continuous phase. So increase in viscosity of the continuous phase by adding thickening agents can reduce the rate of creaming.
Factor affecting viscosity of Viscosity :
Viscosity of continuous phase : Is directly proportional to the viscosity of continuous phase. .Clays and gums increase the viscosity of continuous phase. For w/o emulsions addition of polyvalent metal soaps or use of high melting waxes and resins in the oil phase can be used to increase the viscosity.
Volume of internal phase : Depends upon the volume of internal phase. More the volume of internal phase greater is the viscosity.
Particle size of dispersed phase : On the particle size of dispersed phase Smaller the globule size, more will be the viscosity. That is why emulsion stability can be improved by reduction in globule size.
iii.Coalescence (Cracking ):
It is the process in which the emulsified particles join to form larger particles. The major factor which prevents coalescence is the mechanical strength of electrical barrier. That is why natural gums and proteins are so useful as auxiliary emulsifiers when used at low level , but can even be used a primary emulsifiers at high concentration.
Reasons for( Coalescence) cracking :
Globule size : If globule size is big, ( more than 1-3 µm), emulsion may first cream and then crack. A homogenizer can reduce the size of globules.
Storage Temperature : Extremes of temperature can lead to cracking. When water freezes, it expands , so undue pressure is expected on dispersed globules and the emulsifying film., which may lead to cracking. On the other hand, increase in temperature decreases the viscosity of the continuous phase and disrupts the integrity of interfacial film. An increasing number of collisions between droplets will also occur, leading to increased creaming and cracking.
Changes which affect the interfacial film : These may be physical, chemical or biological effects.
Addition of a common solvent.
Microbial contamination may destroy the emulsifying agent.
Addition of a emulsifying agent of opposite nature for example cationic to anionic.
Incorporation of excess disperse phase : Increasing the quantity of continuous phase will increase the concentration of globules and lead to their
Chemical instability ( Stability )
This may be due to
Oxidation
Hydrolysis
Microbial growth.
iii.Coalescence (Cracking ):
It is the process in which the emulsified particles join to form larger particles. The major factor which prevents coalescence is the mechanical strength of electrical barrier. That is why natural gums and proteins are so useful as auxiliary emulsifiers when used at low level , but can even be used a primary emulsifiers at high concentration.
Reasons for( Coalescence) cracking :
Globule size : If globule size is big, ( more than 1-3 µm), emulsion may first cream and then crack. A homogenizer can reduce the size of globules.
Storage Temperature : Extremes of temperature can lead to cracking. When water freezes, it expands , so undue pressure is expected on dispersed globules and the emulsifying film., which may lead to cracking. On the other hand, increase in temperature decreases the viscosity of the continuous phase and disrupts the integrity of interfacial film. An increasing number of collisions between droplets will also occur, leading to increased creaming and cracking.
Changes which affect the interfacial film : These may be physical, chemical or biological effects.
Addition of a common solvent.
Microbial contamination may destroy the emulsifying agent.
Addition of a emulsifying agent of opposite nature for example cationic to anionic.
Incorporation of excess disperse phase : Increasing the quantity of continuous phase will increase the concentration of globules and lead to their
Chemical instability ( Stability )
This may be due to
Oxidation
Hydrolysis
Microbial growth.
Flocculation :
Flocculation is defined as the association of particle within an emulsion to form large aggregates. However these aggregates can easily be redispersed upon shaking. It is considered as a precursor to the irreversible coalescence. It differs from coalescence mainly in that interfacial film and individual droplets remain intact. Flocculation is influenced by the charges on the surface of the emulsified globules. The reversibility of flocculation depends upon strength of interaction between particles as determined by
a the chemical nature of emulsifier,
b the phase volume ratio,
c. the concentration of dissolved substances, specially electrolytes and ionic emulsifiers.
Flocculation :
Flocculation is defined as the association of particle within an emulsion to form large aggregates. However these aggregates can easily be redispersed upon shaking. It is considered as a precursor to the irreversible coalescence. It differs from coalescence mainly in that interfacial film and individual droplets remain intact. Flocculation is influenced by the charges on the surface of the emulsified globules. The reversibility of flocculation depends upon strength of interaction between particles as determined by
a the chemical nature of emulsifier,
b the phase volume ratio,
c. the concentration of dissolved substances, specially electrolytes and ionic emulsifiers.
ii. Creaming and sedimentation :
The upward or down ward movement of dispersed droplets is termed creaming or sedimentation respectively. In any emulsion, creaming or sedimentation takes place depending on the densities of disperse and continuous phases. Creaming or sedimentation is undesirable as it may lead to coalescence.
Factors affecting rate of creaming :
Rate of creaming is governed by Stoke’s law. As per Stoke’s law
=2r 2(ρ1 - ρ2 ) g / 9η
υ = rate of creaming or sedimentation
r = radius of droplets of dispersed phase
ρ1 , ρ2 = density of dispersed and continuous phase respectively
g = gravitational rate constant
η = viscosity of continuous phase.
Droplet size :
As per Stoke’s law, rate of creaming is directly proportional to the square of radius or diameter of the droplet size. Smaller is the diameter of the droplet, lesser will be the rate of creaming. So reduction in droplet size helps in reducing creaming or sedimentation.
Difference in densities of dispersed and continuous phase :
As per Stoke’s law no creaming is possible if densities of the two phases are equal. So Creaming can be avoided by adjusting the density of dispersed phase.
Viscosity of the continuous phase :
As per Stoke’s law, rate of creaming is inversely proportional to viscosity of the continuous phase. So increase in viscosity of the continuous phase by adding thickening agents can reduce the rate of creaming.
Factor affecting viscosity of Viscosity :
Viscosity of continuous phase : Is directly proportional to the viscosity of continuous phase. .Clays and gums increase the viscosity of continuous phase. For w/o emulsions addition of polyvalent metal soaps or use of high melting waxes and resins in the oil phase can be used to increase the viscosity.
Volume of internal phase : Depends upon the volume of internal phase. More the volume of internal phase greater is the viscosity.
Particle size of dispersed phase : On the particle size of dispersed phase Smaller the globule size, more will be the viscosity. That is why emulsion stability can be improved by reduction in globule size.
