EMULSIONSEMULSIONSKh Sadique Kh Sadique

FaisalFaisalAsst. LecturerAsst. Lecturer

Northern Northern University University

BangladeshBangladesh

EMULSIONSEMULSIONSKh Sadique Kh Sadique

FaisalFaisalAsst. LecturerAsst. Lecturer

Northern Northern University University

BangladeshBangladesh

EMULSIONSEMULSIONS Introduction Introduction Types of emulsionsTypes of emulsions Emulsifying agentsEmulsifying agents Methods of Preparation of EmulsionsMethods of Preparation of Emulsions Tests for emulsion typesTests for emulsion types Emulsion Stability Emulsion Stability Phase InversionPhase Inversion Emulsion BreakingEmulsion Breaking General GuidelinesGeneral Guidelines

An emulsion is a dispersion in which An emulsion is a dispersion in which the dispersed phase is composed of the dispersed phase is composed of small globules of a liquid distributed small globules of a liquid distributed throughout a vehicle in which it is throughout a vehicle in which it is immiscible.immiscible.

IntroductionIntroduction

EMULSIONSEMULSIONSEMULSIONSEMULSIONS

Based on dispersed phase Oil in Water (O/W): Oil droplets dispersed in water Water in Oil (W/O): Water droplets dispersed in oil

Classification of Classification of emulsions :emulsions :

Based on size of liquid droplets 0.2 – 50 mm Macroemulsions (Kinetically Stable) 0.01 – 0.2 mm Microemulsions (Thermodynamically Stable)

Emulsions encountered in everyday lifeEmulsions encountered in everyday life ! !

Metal cutting oils Margarine Ice cream

Pesticide Asphalt Skin cream

Stability of emulsions may be engineered to Stability of emulsions may be engineered to vary from seconds to years depending on vary from seconds to years depending on

applicationapplication

General Types of Pharmaceutical General Types of Pharmaceutical Emulsions:Emulsions:

1) Lotions 1) Lotions 2) Liniments2) Liniments 3) Creams3) Creams 4) Ointments4) Ointments 5) Vitamin drops5) Vitamin drops

Theories of EmulsificationTheories of Emulsification:: 1) Surface Tension Theory:1) Surface Tension Theory:

- lowering of interfacial tension.- lowering of interfacial tension. 2) Oriented-Wedge Theory:2) Oriented-Wedge Theory:

- mono molecular layers of - mono molecular layers of emulsifying agents are curved emulsifying agents are curved around a droplet of the internal around a droplet of the internal phase of the emulsion.phase of the emulsion. 3) Interfacial film theory:3) Interfacial film theory:

- A film of emulsifying agent - A film of emulsifying agent prevents the contact and prevents the contact and coslescing of the dispersed phase.coslescing of the dispersed phase.

Emulsifying Agents:Emulsifying Agents:It is a substance which stabilizes an It is a substance which stabilizes an emulsion .emulsion .

Pharmaceutically acceptable emulsifiers must also : be stable . be compatible with other ingredients . be non – toxic . possess little odor , taste , or color . not interfere with the stability of efficacy of the active agent .

Emulsifying AgentsEmulsifying Agents:: 1) Carbohydrate Materials:1) Carbohydrate Materials:

- Acacia, Tragacanth, Agar, Pectin. o/w - Acacia, Tragacanth, Agar, Pectin. o/w emulsion.emulsion.

2) Protein Substances:2) Protein Substances:

-Gelatin, Egg yolk, Caesin o/w -Gelatin, Egg yolk, Caesin o/w emulsion.emulsion.

3) High Molecular Weight Alcohols:3) High Molecular Weight Alcohols:

- Stearyl Alcohol, Cetyl Alcohol, - Stearyl Alcohol, Cetyl Alcohol, Glyceryl Mono stearate o/w emulsion, Glyceryl Mono stearate o/w emulsion, cholesterol w/o emulsion.cholesterol w/o emulsion.

4) Wetting Agents:4) Wetting Agents:

Anionic, Cationic, NonionicAnionic, Cationic, Nonionic

o/w emulsiono/w emulsion

w/o emulsionw/o emulsion 5) Finely divided solids:5) Finely divided solids:

Bentonite, Magnesium Bentonite, Magnesium Hydroxide, Aluminum Hydroxide, Aluminum Hydroxide o/w emulsion.Hydroxide o/w emulsion.

Methods of Preparation of Methods of Preparation of Emulsions:Emulsions:

1) Continental or Dry Gum Method:1) Continental or Dry Gum Method:

"4:2:1" Method"4:2:1" Method

4 parts (volumes) of oil4 parts (volumes) of oil

2 parts of water2 parts of water

1 part of gum1 part of gum

2) English or wet Gum Method:2) English or wet Gum Method:

4 parts (volumes) of oil4 parts (volumes) of oil

2 parts of water2 parts of water

1 part of gum1 part of gum

3) Bottle or Forbes Bottle Method:3) Bottle or Forbes Bottle Method: useful for extemporaneous preparation useful for extemporaneous preparation

of emulsion from volatile oils or of emulsion from volatile oils or oleaginous substance of low viscosity.oleaginous substance of low viscosity.

powdered acaciapowdered acacia

+ Dry bottle+ Dry bottle

2 parts of oil2 parts of oil

This method is not suitable for viscous This method is not suitable for viscous oils (i.e. high viscosity oil).oils (i.e. high viscosity oil).

Emulsion Type and Means of Emulsion Type and Means of Detection:Detection:

Tests for Emulsion Type (W/O or O/W Tests for Emulsion Type (W/O or O/W emulsions)emulsions)

1) Dilution Test:1) Dilution Test:

- o/w emulsion can be diluted with - o/w emulsion can be diluted with water.water.

- w/o emulsion can be diluted with - w/o emulsion can be diluted with oil.oil.

2) Conductivity Test:2) Conductivity Test:

Continuous phase water > Continuous phase oil.Continuous phase water > Continuous phase oil.

4) Refractive index measurement4) Refractive index measurement

5) Filter paper test5) Filter paper test

3) Dye-Solubility Test:3) Dye-Solubility Test:

- water soluble dye will dissolve in - water soluble dye will dissolve in the aqueous phase.the aqueous phase.

- oil soluble dye will dissolve in the oil - oil soluble dye will dissolve in the oil phase.phase.

Emulsions are Kinetically Stable!Emulsions are Kinetically Stable!

Rate of coalescence Rate of coalescence –– measure of emulsion measure of emulsion stability. stability.

It depends on:It depends on:

(a)(a) Physical nature of the interfacial Physical nature of the interfacial surfactant filmsurfactant film

For Mechanical stability, surfactant films are For Mechanical stability, surfactant films are characterized characterized

by strong lateral intermolecular forces and high by strong lateral intermolecular forces and high elasticity elasticity

(Analogous to stable foam bubbles)(Analogous to stable foam bubbles)

(b)(b) Electrical or steric barrier Electrical or steric barrier

Significant only in O/W emulsions. Significant only in O/W emulsions. In case of non-ionic emulsifying agents, charge In case of non-ionic emulsifying agents, charge

may arise due to may arise due to (i) adsorption of ions from the aqueous phase or(i) adsorption of ions from the aqueous phase or (ii) contact charging (phase with higher dielectric (ii) contact charging (phase with higher dielectric

constant is charged positively)constant is charged positively)

No correlation between droplet charge and No correlation between droplet charge and emulsion stability in W/O emulsionsemulsion stability in W/O emulsions

Steric barrier Steric barrier –– dehydration and change in dehydration and change in hydrocarbon chain conformation.hydrocarbon chain conformation.

(c) (c) Viscosity of the continuous phaseViscosity of the continuous phase

(many emulsion are more stable in concentrated (many emulsion are more stable in concentrated form than when diluted.)form than when diluted.)

Viscosity may be increased by adding natural or Viscosity may be increased by adding natural or synthetic thickening agents.synthetic thickening agents.

(d) (d) Size distribution of dropletsSize distribution of droplets

Emulsion with a fairly uniform size distribution Emulsion with a fairly uniform size distribution is more stableis more stable

(e) (e) Phase volume ratioPhase volume ratio

As volume of dispersed phase As volume of dispersed phase stability of stability of emulsion emulsion

(eventually phase inversion can occur)(eventually phase inversion can occur)

(f) (f) TemperatureTemperature

Temperature Temperature , usually emulsion stability , usually emulsion stability Temp affects Temp affects –– Interfacial tension, Interfacial tension, D,D, solubility solubility of surfactant, viscosity of liquid, phases of of surfactant, viscosity of liquid, phases of interfacial film.interfacial film.

Inversion of Emulsions (Phase Inversion of Emulsions (Phase inversion)inversion)

O/WO/W W/O W/O

1.1. The order of addition of the phasesThe order of addition of the phasesW W O + emulsifier O + emulsifier W/O W/OO O W + emulsifier W + emulsifier O/W O/W

2.2. Nature of emulsifierNature of emulsifierMaking the emulsifier more oil soluble Making the emulsifier more oil soluble tends to produce a W/O emulsion and vice tends to produce a W/O emulsion and vice versa.versa.

3.3. Phase volume ratioPhase volume ratioOil/Water ratioOil/Water ratio W/O emulsion and vice W/O emulsion and vice versaversa

4. Temperature of the system4. Temperature of the system

Temperature of O/W makes the Temperature of O/W makes the emulsifier more hydrophobic and the emulsifier more hydrophobic and the emulsion may invert to W/O.emulsion may invert to W/O.

5. Addition of electrolytes and other 5. Addition of electrolytes and other additives.additives.

Strong electrolytes to O/W (stabilized Strong electrolytes to O/W (stabilized by ionic surfactants) may invert to W/Oby ionic surfactants) may invert to W/O

Example. Inversion of O/W emulsion Example. Inversion of O/W emulsion (stabilized by sodium cetyl sulfate and (stabilized by sodium cetyl sulfate and cholesterol) to a W/O type upon cholesterol) to a W/O type upon addition of polyvalent Ca.addition of polyvalent Ca.

Separation of the internal phase from Separation of the internal phase from the external phase is called the external phase is called BREAKINGBREAKING of the emulsion. This is irreversible.of the emulsion. This is irreversible.

Protect emulsions against the extremes Protect emulsions against the extremes of cold and heat.of cold and heat.

Emulsions may be adversely affected by Emulsions may be adversely affected by microbial contamination.microbial contamination.

Emulsion Emulsion BreakingBreaking

General Guidelines:General Guidelines:

1.1. Type of emulsion determined by the phase Type of emulsion determined by the phase in which emulsifier is placed.in which emulsifier is placed.

2.2. Emulsifying agents that are preferentially Emulsifying agents that are preferentially oil soluble form W/O emulsions and vice oil soluble form W/O emulsions and vice versa.versa.

3.3. More polar the oil phase, the more More polar the oil phase, the more hydrophilic the emulsifier should be. More hydrophilic the emulsifier should be. More non-polar the oil phase more lipophilic the non-polar the oil phase more lipophilic the emulsifier should be.emulsifier should be.