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UNIVERSITY OF NIZWA COLLEGE OF PHARMACY AND NURSING
SCHOOL OF PHARAMCY
PHYSICAL PHARMACY: PHCY102 LECTURER: COARSE DISPERSION
SUBTITLE: EMULSIONS
DR. JAGADEESH G HIREMATH
Assistant professor in Pharmaceutics School of Pharmacy University of Nizwa
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Emulsions are colloidal dispersions in which a liquid is dispersed in a continuous liquid phase of different composition. The dispersed phase is sometimes referred to as the internal (disperse) phase and the continuous phase as the external phase.
oil-in-water (O/W) for oil droplets dispersed in water water-in-oil (W/O) for water droplets dispersed in oil
CLASSIFICATION OF EMULSIONS
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Pharmaceutical application of emulsions:
1. Oral, rectal and topical administration of oils and oil-
soluble drugs.
2. The unpleasant taste or odor can be masked by
emulsification
3. Intramuscular injections of water-soluble drugs or
vaccine to provide slow release.
4. The use of sterile stable i.v emulsion containing fats,
carbohydrates and vitamins as a potential nutrition
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Water in oil emulsion (w/o)
Oil in water emulsion (o/w)
Oil is the dispersion medium and water is
the dispersed phase
Water is the dispersion medium and oil is
the dispersed phase
They are greasy and not water washable They are non greasy and easily removable
from the skin surface
They are used externally to prevent
evaporation of moisture from the surface of
skin e.g. Cold cream
They are used externally to provide
cooling effect e.g. vanishing cream
Oil soluble drugs are more quickly released
from w/o emulsions
Water soluble drugs are more quickly
released from o/w emulsions
They are preferred for formulations
meant for external use like creams.
They are preferred for formulations
meant for internal use as bitter taste of
oils can be masked.
W/O emulsions go not give a positive
conductivity test as oil is the external phase
which is a poor conductor of electricity.
O/W emulsions give a positive
conductivity test as water is the external
phase which is a good conductor of
electricity.
DIFFERENCE BETWEEN O/W AND W/O EMULSIONS
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TEST FOR IDENTIFICATION OF EMULSION TYPE:
Dilution test (miscibility test)
Staining test (dye solubility test)
Conductivity measurement
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Conductivity Test
This test is based on the basic principle that water is a good conductor
of electricity. Therefore in case of o/w emulsion , this test will be
positive as water is the external phase. In this test. An assembly
consisting of a pair of electrodes connected to a lamp is dipped into an
emulsion. If the emulsion is o/w type, the lamp glows.
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Dye Solubility Test
In this test, when an emulsion is mixed with a water soluble dye such as
amaranth and observed under the microscope, if the continuous phase
appears red, then it means that the emulsion is o/w type as water is the
external phase and the dye will dissolve in it to give color but if the scattered
globules appear red and continuous phase colorless, then it is w/o type.
Similarly if an oil soluble dye such as Scarlet red C or Sudan III is added to
an emulsion and the continuous phase appears red, then it w/o emulsion.
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CLASSIFICATION OF EMULSIFYING AGENTS
Surface active agents
These are adsorbed at oil-water interfaces to form
monomolecular films and reduce interfacial tension.
Hydrophilic colloids:
These are form multimolecualr films around the dispersed
droplets of oil in a o/w emulsion
Finely divided solid particles:
These are adsorbed at the interface between two immiscible
liquid phases and form a film of particles around the
dispersed globules.
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Name Class Type of
emulsion
formed
Tritethylene amine oleate Surface active agent
anionic
o/w (HLB=12)
Sorbitan monooleate (S-80) Surface active agent
nonionic
w/o (HLB=4.3)
Polyoxyethyelene sorbitan
Monooleate (T-80)
Surface active agent
(nonionic)
o/w (HLB=15)
Acacia Hydrophilic colloid o/w
Gelatin Hydrophilic colloid o/w
Bentonite Solid particle o/w & w/o
Veegum Solid particle o/w
TYPICAL EMULSIFYING AGENTS
WHAT ARE SURFACE ACTIVE AGENTS
These are solutes which are adsorbed at
the surface or interface of liquid and
reduce the surface or interfacial tension
and therefore termed Surface active agent,
surfactants or amphiphile.
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A lipophilic (hydrophobic) group consisting of a long
carbon chain which has little affinity for aqueous
solvents.
A hydrophilic (or lipopophobic) group consisting of
polar group such as COOH, OH,…which has high
affinity for polar solvents.
SURFACE ACTIVE AGENTS CONSISTS OF 2
PARTS:
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WHAT IS SURFACE ACTIVE AGENT
Surfactant will make proper balance between their
hydrophilic and lipophilic properties so that they can
stay at the interface.
When the S.A.A. dissolved in water: it will be oriented
as follow:
Hydrophilic part ”polar” directed inward toward the water bulk.
Lipophilic part ”non polar” directed upward.
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Hydrophilic SAA (HLB > 10)
Lipophilic SAA ( HLB 1-10)
HLB = 0 implies 100% hydrophobic
HLB = 20 implies 100% hydrophilic.
In this system , each surfactant is assigned a number between 1 and 20 representing the relative proportions of lipophilic and hydrophilic parts of the molecule.
The higher the number, the more hydrophilic the surfactant.
SURFACE ACTIVE AGENTS DIVIDED ACCORDING TO HLB
VALUES
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A SCALE SHOWING CLASSIFICATION OF SURFACTANT FUNCTION ON THE BASIS OF HLB VALUES
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FLOCULATION AND CREAMING
COALESCENCE AND BREAKING
PHASE INVERSION
PROBLEMS IN EMULSIONS
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FLOCULATION AND CREAMING
This factor is related by stokes low
V= d2 (ρs- ρo ) g
18o
Analysis of this equation show that, if the dispersed phase is less
dense than the continuous phase which is occurs generally in o/w
emulsions, the velocity of the sedimentation becomes negative, then
creaming in upward direction.
If the internal phase is heavier than the external phase, the
globules settle occurs in w/o emulsions this is called creaming in a
downward direction. This occurs because internal aqueous phase is
denser than the continuous oil phase.
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HOW TO SOLVE UPWARD AND DOWNWARD
FLOCCUALTION AND CREAMING
By adding the viscosity improver or thickening
agent
Exp: methylcellulose, tragacanth, sodium alginate
Particle size of the globules can be reduced by
homogenization.
SO CREAMING IS REVERSIBLE PROCESS
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COALESCENCE AND BREAKING
Breaking occurs due to simple mixing fails to resuspend the
globules, in a stable emulsified form because the film surrounding
the particles has been destroyed and oil tends to coalesce
(separation)
The dispersion is non uniform, the small particles will going to
attached one another and form larger particles becomes strong
cohesion so that internal phase can separate easily.
SO COALESCENCE AND BREAKING IS
NOT REVERSIBLE PROCESS
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PHASE INVERSION
An o/w emulsion stabilized with sodium stearate can be
inverted to w/o type by adding calcium chloride to form
calcium stearate.
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THEORY OF EMULSIONS
Surface Tension Theory
HARKINS Oriented-Wedge Theory
Adsorbed-interfacial film theories
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What is Surface Tension Theory
Surface tension is a result of attractive cohesive forces
between molecules adjacent at the surface and below
Tension between two immiscible liquids is called
interfacial tension.
According to the surface tension theory, an emulsion
may be formed of two immiscible liquids if an agent that
lowers the interfacial tension is added to the system.
A surfactant, due to the molecular character, settles at
the interfaces of oil and water.
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WHAT IS HARKINS’ ORIENTED WEDGE THEORY
According to the oriented wedge theory, the difference in
the relative size of the polar and non-polar groups of the
surfactant explains the type of the formed emulsion. The
group with the larger cross sectional area will be oriented
outside of the droplet.
For example, the greater cross sectional area of the polar
rather than the non-polar group will produce an o/w
emulsion.
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WHAT IS ADSORBED-INTERFACIAL
FILM THEORIES
A film of emulsifying agent prevents the
contact and coalescing of the dispersed
phase.
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REQUIREMENT FOR PHARMACEUTICAL
EMULSION PREPARATIONS
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EMULSIFYING AGENTS
Carbohydrate Materials:
Acacia, Tragacanth, Agar, Pectin. o/w emulsion.
Protein Substances:
Gelatin, Egg yolk, Caesin o/w emulsion.
High Molecular Weight Alcohols:
Stearyl Alcohol, Cetyl Alcohol, Glyceryl Mono stearate
o/w emulsion, cholesterol w/o emulsion.
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WETTING AGENTS
Anionic
Cationic
Nonionic
FINELY DIVIDED SOLIDS:
Bentonite, Magnesium Hydroxide,
Aluminum Hydroxide o/w emulsion
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THANK YOU ONE ALL