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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