EMULSIONS : EMULSIONS Slide 2: EMULSIONS Introduction
Types of emulsions
Methods of Preparation of Emulsions
Tests for emulsion types
General Guidelines Slide 3: An emulsion is a dispersion in which the dispersed phase is composed of small globules of a liquid distributed throughout a vehicle in which it is immiscible. Introduction EMULSIONS Slide 4: 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 emulsions : Based on size of liquid droplets
0.2 – 50 mm Macroemulsions (Kinetically Stable)
0.01 – 0.2 mm Microemulsions (Thermodynamically Stable) Slide 5: Emulsions encountered in everyday life! Stability of emulsions may be engineered to vary from seconds to years depending on application Slide 6: General Types of Pharmaceutical Emulsions:
5) Vitamin drops Slide 7: Theories of Emulsification:
1) Surface Tension Theory:
- lowering of interfacial tension.
2) Oriented-Wedge Theory:
- mono molecular layers of emulsifying agents are curved around a droplet of the internal phase of the emulsion. 3) Interfacial film theory:
- A film of emulsifying agent prevents the contact and coslescing of the dispersed phase. Slide 8: Emulsifying Agents:
It is a substance which stabilizes an 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 . Slide 9: Emulsifying Agents:
1) Carbohydrate Materials:
- Acacia, Tragacanth, Agar, Pectin. o/w emulsion.
2) Protein Substances:
-Gelatin, Egg yolk, Caesin o/w emulsion.
3) High Molecular Weight Alcohols:
- Stearyl Alcohol, Cetyl Alcohol, Glyceryl Mono stearate o/w emulsion, cholesterol w/o emulsion. Slide 10: 4) Wetting Agents:
Anionic, Cationic, Nonionic
5) Finely divided solids:
Bentonite, Magnesium Hydroxide, Aluminum Hydroxide o/w emulsion. Slide 11: Methods of Preparation of Emulsions:
1) Continental or Dry Gum Method:
4 parts (volumes) of oil
2 parts of water
1 part of gum Slide 12: 2) English or wet Gum Method:
4 parts (volumes) of oil
2 parts of water
1 part of gum Slide 13: 3) Bottle or Forbes Bottle Method:
useful for extemporaneous preparation of emulsion from volatile oils or oleaginous substance of low viscosity.
+ Dry bottle
2 parts of oil
This method is not suitable for viscous oils (i.e. high viscosity oil). Slide 14: Emulsion Type and Means of Detection:
Tests for Emulsion Type (W/O or O/W emulsions)
1) Dilution Test:
- o/w emulsion can be diluted with water.
- w/o emulsion can be diluted with oil. 2) Conductivity Test:
Continuous phase water > Continuous phase oil. Slide 15: 4) Refractive index measurement
5) Filter paper test 3) Dye-Solubility Test:
- water soluble dye will dissolve in the aqueous phase.
- oil soluble dye will dissolve in the oil phase. Slide 16: Emulsions are Kinetically Stable!
Rate of coalescence – measure of emulsion stability.
It depends on:
Physical nature of the interfacial surfactant film
For Mechanical stability, surfactant films are characterized
by strong lateral intermolecular forces and high elasticity
(Analogous to stable foam bubbles) Slide 17: (b) Electrical or steric barrier
Significant only in O/W emulsions.
In case of non-ionic emulsifying agents, charge may arise due to
(i) adsorption of ions from the aqueous phase or
(ii) contact charging (phase with higher dielectric constant is charged positively)
No correlation between droplet charge and emulsion stability in W/O emulsions
Steric barrier – dehydration and change in hydrocarbon chain conformation. Slide 19: (d) Size distribution of droplets
Emulsion with a fairly uniform size distribution is more stable
(e) Phase volume ratio
As volume of dispersed phase stability of emulsion
(eventually phase inversion can occur)
Temperature , usually emulsion stability
Temp affects – Interfacial tension, D, solubility of surfactant, viscosity of liquid, phases of interfacial film. Slide 20: Inversion of Emulsions (Phase inversion)
The order of addition of the phases
W O + emulsifier W/O
O W + emulsifier O/W
Nature of emulsifier
Making the emulsifier more oil soluble tends to produce a W/O emulsion and vice versa.
Phase volume ratio
Oil/Water ratio W/O emulsion and vice versa Slide 21: 4. Temperature of the system
Temperature of O/W makes the emulsifier more hydrophobic and the emulsion may invert to W/O.
5. Addition of electrolytes and other additives.
Strong electrolytes to O/W (stabilized by ionic surfactants) may invert to W/O
Example. Inversion of O/W emulsion (stabilized by sodium cetyl sulfate and cholesterol) to a W/O type upon addition of polyvalent Ca. Slide 22: Separation of the internal phase from the external phase is called BREAKING of the emulsion. This is irreversible.
Protect emulsions against the extremes of cold and heat.
Emulsions may be adversely affected by microbial contamination. Emulsion Breaking Slide 23: General Guidelines:
Type of emulsion determined by the phase in which emulsifier is placed.
Emulsifying agents that are preferentially oil soluble form W/O emulsions and vice versa.
More polar the oil phase, the more hydrophilic the emulsifier should be. More non-polar the oil phase more lipophilic the emulsifier should be. Slide 24: إعداد وتقديم : ندى العصيمي سلطانة الفغم زينة العبد الكريم غادة الحمود