(Emulsion 2)

An emulsion is a mixture of two or more liquids that are normally immiscible. Emulsions are part of a more general class of two-phase systems of matter called colloids.

1. Emulsions 2
Md. Saiful Islam
BPharm, MPharm(PCP)
North South University
Fb Group: Pharmacy Universe

2. Theories of emulsification
•The most prevalent theories to explain how emulsifying
agents promote emulsification and maintain the stability
of the emulsion are:
-the surface tension theory
-the oriented-wedge theory
-the plastic or interfacial film theory

3. The surface tension theory of emulsification
•The use of surface active (surfactant) or wetting agents
as emulsifier and stabilizer
-lowers the interfacial tension of the two immiscible
liquid
-reduces the repellent force between the liquids
-diminishes each liquid’s attraction for its own
molecules
•Thus the surface-active agents facilitate the breaking up
of large globules into smaller ones, which then have a
lesser tendency to reunite or coalesce

4. The oriented-wedge theory of emulsification
•The theory is based on the presumption that certain
emulsifying agents orient themselves about and within a
liquid in a manner reflective of their solubility in that
particular liquid.
•The molecules of substances upon which this theory is
based,have a hydrophilic and hydrophobic( usually
lipophilic or oil loving) portion and they position or orient
themselves into each phase

5. The oriented-wedge theory of emulsification
•The wedge shape envisioned for the molecules causes
either oil globules or water globules to be surrounded
•The phase in which the emulsifying agent is more
soluble will become the continuous or external phase of
the emulsion
•In practice, it is generally found that water soluble
emulsifier do form o/w emulsions and vice versa

6. The plastic or interfacial film theory
of emulsification
•The emulsifying agent surrounds the droplets of the
internal phase as a thin layer of film adsorbed on the
surface of the drops
•The film prevents contact and coalescing of the
dispersed phase
•The tougher and more pliable the film, the greater the
stability of the emulsion
•Water-soluble emulsifying agent encourages o/w
emulsions formation and oil-soluble emulsifiers the
reverse

7. •Finally we can say that a single theory of emulsification
cann’t explain all the mechanisms of emulsifiers.In a
given emulsion system, more than one theory may play
a part
•However, lowering of the interfacial tension is important
in the initial formation of an emulsion, but the formation
of a protective wedge of molecules or film of emulsifier is
also important for continued stability. Certain emulsifiers
are capable of both tasks

8. Emulsifying agents
Desirable properties:
1.It should be surface active, at least to the extent that
the interfacial tension is reduced to less than 10
dynes/cm
2.It should be rapidly adsorbed around the dispersed
droplets and form a coherent film capable of
preventing coalescence

9. Desirable properties of emulsifying
agents
3. It should result in the formation of an electrical potential
at the droplet surface adequate to ensure repulsion
between approaching droplets
4. It should increase the viscosity of the emulsion as a
means of enhancing stability
5. It should be effective in a fairly low concentration

10. Types of Emulsifying Agents
1)Synthetic emulsifying agents:
•Superior to natural ones because they are not
susceptible to decomposition by micro-organisms
•The ratio of hydrophilic and lipophilic groups in the
molecule may be altered, which is advantageous for
externally applied emulsions
•Only a limited number of synthetic agents are safe for
internal use. These are-
-the sorbitan esters ( Spans)
-the polyoxyethylene sorbitan esters
( Tweens) and
-purified glyceryl monostearate

11. Types of Synthetic emulsifying agents
Three types-
-Non-ionic, where the entire undissociated molecule
provides emulsifying action
-Anionic, where the anion provides emulsifying action
-Cationic, where the cation provides emulsifying
action

12. Non-ionic emulsifying agents
-The entire undissociated molecule having a balanced
hydrophilic and lipophilic groups
-Not susceptible to pH changes and the presence of
electrolytes
-The best results are often obtained by using the
combination of a predominantly lipophilic agent (a Span)
and a predominantly hydrophilic agent (a Tween)

13. Non-ionic emulsifying agents
•Examples are:
-Sorbitan monooleate (Span 80)
-Sorbitan monolaurate (Span 20)
-Polyoxyethylene sorbitan monooleate (Tween80)
-Polyoxyethylene sorbitan monolaurate (Tween20)

14. Anionic emulsifying agents
•This group includes:
-monovalent, polyvalent and organic soaps
-sulfated alcohols and
-sulfonates
Soaps:
•Being salts of long chain fatty acids, have a disagreeable
taste and produce an irritating and laxative action in the
intestinal tract –so not used in orally administered
emulsions

15. Soaps
-The alkali soaps are hydrophilic (eg. Na, K and NH
4salt
of lauric, myristic, plamitic, stearic and oleic acids)
and promotes o/w emulsion
-The metallic soaps are water-insoluble and promotes
w/o emulsion (eg. Ca, Mg, Zn, Pb and Al salts of fatty
acids)
-Organic soaps produce o/w emulsions
(eg.Triethanolamine oleate)
These soaps:
-practically neutral in reaction(pH-8)
-represent a better balance between hydrophilic
and lipophilic groups

16. Sulfated alcohols and Sulfonates
•Sulfated alcohols are used as o/w emulsifying agents
with an auxiliary agents. They are easily hydrolyzed.
Example-sodium lauryl alcohol
•Sulfonates have a higher tolerance to calcium ions and
do not readily hydrolyze
Example-sodium dioctyl sulfosuccinate

17. Cationic emulsifying agents
•Besides emulsifying action, these agents have marked
bactericidal action
•Anionic agents must not be used in combination with it.
•Examples are:
-Benzalkonium chloride
-N-cetyl N-ethyl morpholinium ethosulfate

18. 2) Natural emulsifying agents
•Most of the natural emulsifying agents form o/w emulsion
•They are non toxic
•They are used in the preparation of oral and parenteral
emulsions
•Examples are:
-Acacia
-Gelatin
-Cholesterol
-Wool fat and derivatives

19. Acacia
•The only true emulsifying agent of the natural gum class
•Particularly useful for preparing emulsions in a morter
•Not viscous enough to prevent rapid rise of the globules
•A creamy layer is formed on the surface of the emulsion
•Thickening agents (eg. Agar, tragacanth) are used to
minimize the creaming effect
•Emulsion prepared with acacia are stable over a pH
range 2-10
•Preservatives are needed to add with it

20. Finely divided solids as emulsifying
agents
•These agents produce a coherent film around the
globules at the interface and prevent coalescence of the
internal phase
•Which are easily wetted by water form o/w emulsions
•Which are easily wetted preferentially by oil tended to
produce w/o emulsions

21. Finely divided solids as emulsifying
agents
Examples are:
-Bentonite
-Veegum
-Mg(OH)
2
-Al(OH)
3
-MgO
-Silica gel

22. Auxiliary emulsifying agents
•These are normally incapable themselves of forming
stable emulsion
•Based on their thickening action, they assist the primary
emulsifier to enhance the stability of the product
•Examples are:
-Agar
-pectin
-tragacanth
-silica gel
-sodium carboxy methyl cellulose

23. Mixed emulsifying agents
•Frequently consists of a blend of emulsifiers
•Provides the proper hydrophilic-lipophilic nature
•Establishes a stable film at the interface
•Supplies the desired consistency to the product
•Contributes certain other properties such emolliency,
spreading and deflocculation

24. Mixed emulsifying agents
•Auxiliary agents may be mixed with primary emulsifiers
Example: Agar and Tragacanth are frequently combined
with Acacia
•Primary emulsifiers of water-in-oil type may be mixed
with oil-in-water type
Example: Lecithin (o/w type) can be mixed with
cholesterol (w/o type)
•Sometimes a complex of emulsifying agent is made to
improve emulsifying action
Example: Emulsifying action of sodium oleate is
improved by combination with cetyl alcohol, cholesterol
and similar lipophilic agents