introduction to emulsion, Emulsion theories

1. Theories of
Emulsification
Dr.Monika Nijhawan

2. Def:
Emulsions are two phase systems in which the dispersed
phase is also a liquid. They are also termed as biphasic
systems or heterogeous systems.

3. EMULSIONS
Methods of Preparation of Emulsions:
1) Continental or Dry Gum Method:
"4:2:1" Method
4 parts (volumes) of oil [Ansel. page 275]
2 parts of water
1 part of gum

4. EMULSIONS
2) English or wet Gum Method:
4 parts (volumes) of oil
2 parts of water
1 part of gum

5. EMULSIONS
3) Bottle or Forbes Bottle Method:
useful for extemporaneous preparation of
emulsion from volatile oils or oleaginous
substance of low viscosity.
powdered acacia
+ Dry bottle
2 parts of oil
This method is not suitable for viscous oils

6. EMULSIONS
Stability of Emulsion:
• An emulsion is considered to be physically
unstable if :
a) The internal phase tends to form aggregates
of globules.
b) Large globules or aggregates of globules rise
to the top or fall to the bottom of the emulsion to
form a concentrated layer of the internal
phase.
c) If all or part of the liquid of the internal phase
becomes "unemulsified on the top or bottom of
the emulsion.

7. EMULSIONS
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.

8. A variety of emulsifying agents are used, each act by
different mechanism.
Monomolecular Adsorption and Film Formation
Multimolecular Adsorption
Solid Particle Adsorption

9. Monomolecular Adsorption and Film Formation
1. Surfactants adsorb at the oil-water interface
and form a monomolecular film. This film
rapidly envelops the droplets as soon as they
are formed. Agents having higher interfacial
activity are better suited for this purpose.
2. Surfactants are capable of reducing the
interfacial tension. This facilitates the
immediate formation of small droplets.
Furthermore, its importance can be understood
by considering the surface free energy
changes during emulsification.
3. Ionic surfactants impart charges on interfacial
films. These films exert repulsive forces
between two approaching globules and prevent
their coalescence.

10. Multimolecular Adsorption
The emulsifying agents
such as acacia and gelatin,
(isoelectric point) tend to form a
multimolecular film around the
globules and prevent coalescence.

11. Solid Particle Adsorption
The finely divided solid particles adsorb
at the oil-water interface and form a rigid
film of closely packed solids.
Ex: Bentonite – o/w &w/o
Veegum – o/w

12. EMULSIONS
Phase Inversion:
• The relative volume of internal and external
phases of an emulsion is important.
• Increase internal concentration Increases
viscosity up to a certain point.
• Viscosity will decrease after that point.
• At this point the emulsion has undergone
inversion i.e. it has changed from an o/w to a
w/o, or vice versa.
• In practice, emulsions may be prepared without
inversion with as much as about 75% of the
vol. of the product being internal phase.

13. Physical instability – Markers
Signs of Instability are:
Flocculation:
Neighbouring globules come closer to each other and
form colonies in the external phase. This phenomenon is clearly
visible. The extent of this depends on:
- Globule size distribution: uniform size
- Charge on the globule surface: Electrolytes, ionic
emusifying agents
- Viscosity of the external medium.:viscosity improving
agents

14. Creaming:
It is the conc. of globules at the top or bottom of the
emulsion. Floccules move either up or down leading to creaming.
It can also be due to movement of individual globules. It is a
reversible process.
Two types:
Upward creaming
Downward creaming

15. Creaming can be prevented by:
1. Reducing the particle size by homogenisation.
2. Increasing the viscosity of external phase.
3. Reducing the differences in densities.
Coalescence:
Few globules tend to fuse with each other and form bigger
globules. It is observed due to
1. insufficient amount of the emulsifying agent.
2. altered partitioning of the emulsifying agent.
3. incompatibilities between emulsifying agents.

16. Breaking:
Is indicated by complete separation of oil and aqueous phases.
It is due to the breaking of protective sheath around the
globules. It is a irreversible process.
Phase Inversion:
Involves change in the emulsion type.

17. THANKS