2. An emulsion is liquid preparation containing two immiscible
liquids, one of which is dispersed as globules (dispersed phase)
in the other liquid (continuous phase).
dispersed phase
continuous phase
Microemulsion : Droplets size range 0.01 to 0.1µm
Macroemulsion : Droplets size range approximately 5µm
An emulsion is a thermodynamically unstable system consisting of at
least two immiscible liquid phases one of which is dispersed as
globules in the other liquid phase stabilized by a third substance
called emulsifying agent.
Emulsions are also called heterogeneous systems or biphasic systems
Two Immiscible Liquids
Dispersed Phase
(Internal phase)
Continuous Phase
(External phase)
3. 3
A
B C D
A.: Two immiscible liquids not emulsified
B. An emulsion of phase A dispersed in Phase B
C. Unstable emulsion slowly separates.
D. The emulsifying agent ( black film) places it self on the interface between
phase A and phase B and stabilizes the emulsion.
Phase A
Phase B
Examples for emulsions:- milk, rubber latex, crude oil etc.
4. 4
Types of emulsions
Simple emulsions (Macro emulsions)
• Oil-in-water (O/W)
• Water-in-oil (W/O)
O/W emulsion W/O emulsion
water is continuous phase
Oil is dispersed phase
oil is continuous phase
water is dispersed phase
8. To mask the taste
O/W is convenient means of orally administration of water-
insoluble liquids
O/W emulsion facilitates the absorption of water-insoluble
compounds comparing to their oily solution preparations (e.g.
vitamins)
Oil-soluble drugs can be given parentrally in form of oil-in water
emulsion. (e.g Taxol)
Emulsion can be used for external application in cosmetic and
therapeutic uses.
9. Dilution test:
In this test the emulsion is diluted either with oil or water. If the emulsion is
o/w type and it is diluted with water, it will remain stable as water is the
dispersion medium" but if it is diluted with oil, the emulsion will break as
oil and water are not miscible with each other.
Add drops of water
Add drops of water
O/W Emulsion W/O Emulsion
Water distribute
Uniformly
o/w emulsion can be diluted with water.
w/o emulsion can be diluted with oil.
using of naked eye, it is very difficult to differentiate between o/w or
w/o emulsions. Thus, the four following methods have been used to
identify the type if emulsions.
10. Bulb glows with O/W Bulb doesn’t glow with W/O
Emulsion Emulsion
Conductivity Test: water is good conductor of electricity whereas
oil is non-conductor. Therefore, continuous phase of water runs
electricity more than continuous phase of oil.
11. O/W EMULSION
W/O EMULSION
Water Soluble Dye Ex. Amaranth Dye
DYE TEST:
water is continuous phase
Oil is dispersed phase
oil is continuous phase
water is dispersed phase
Water-soluble dye will dissolve in the aqueous phase.
12. Oil Soluble Dye Ex. scarlet
O/W EMULSION
W/O EMULSION
water is continuous phase
Oil is dispersed phase
oil is continuous phase
water is dispersed phase
Oil-soluble dye will dissolve in the oil phase.
13. When a w/o emulsion is exposed to fluorescent light
under a microscope the entire field fluorescence. If the
fluorescence is spotty, then the emulsion is of o/w-type.
However, all oils do not exhibit fluorescence under UV
light and thus the method does not have universal
application.
It is necessary that the results obtained by one method
should always be confirmed by means of other methods
14. 5.Creaming test.
The direction of creaming identifies the emulsion type,
if the densities of aqueous and oil phases are known.
Water-in-oil emulsions normally cream downward as oil
is usually less dense than water.
Oil-in-water emulsions normally cream upwards.
15. 6. CoCl2/filter paper test:
• Filter paper impregnated with CoCl2 and dried appear
to be blue but when dipped in o/w emulsion changes to
pink.
• This test may fail if emulsion unstable or breaks in
presence of electrolyte.
16.
17. • When left aside, droplets fuse themselves and finally separate
as two layers.
• This in an indication of instability of an emulsion.
• Except in the case of very dilute oil-in-water emulsions (oil
hydrosols), which are somewhat stable, the liquids separate
rapidly into two clearly defined layers.
18. • The state of instability may be described by the fact that the
cohesive force between the molecules of each separate liquid is
greater than the adhesive force between the two liquids.
• Any attempt to increase the adhesive forces between these phases
can produce a stable emulsion.
• A system is said to be thermodynamically stable, if it possesses low
surface free energy.
• The higher the interfacial area, the greater is the interfacial free
energy, and hence lower the stability.
19. • one of the liquids forms small droplets and gets dispersed in
the other liquid
– As a result, globules possess an enormously enhanced
surface area compared to its original surface area.
Consequently, the interfacial energy increases.
The relationship is as follows.
∆G = γo/w ∆A (1)
Where ∆G = increase in surface free energy
γo/w= interfacial tension of oil-water interface
∆A = increase in surface area of the interface due to
droplet formation
20. 1. The system spontaneously tries to change back to its original
state by decreasing ∆A, so that ∆G will be zero.
The result is the coalescence of globules and separation of
phases. The process of coalescence is undesirable for
physical stability.
thermodynamically unstable
Regrouping of globules can be prevented to a great extent by
adding a third component called emulsifying agents in
emulsions.
21. 2. In equation (1), the interfacial tension, γo/w may be reduced, so
that the system can be stable. But it cannot be made zero,
because the dispersed phases have certain positive interfacial
tension.
Hence the term ∆G cannot be made zero.
However surface active agents are added to reduce γo/w value
to a minimum.
Thus, the system can be stabilized to a certain extent.
Certain emulsifying agents can reduce the surface tension
thereby prevent coalescence.
Such substances are best suited for the preparation of a stable
emulsion.
22. Monomolecular adsorption theory
(a) Reduction in interfacial tension, surface free energy
Surface active agents reduce interfacial tension
because of their adsorption at the oil-water interface to form
monomolecular films.
Surface free energy, W = γo/w x ΔA
γo/w= interfacial tension of oil-water interface
∆A = increase in surface area of the interface due to droplet formation,
we must retain a high surface area for the dispersed phase.
Any reduction in the interfacial tension, γo/w , will reduce the
surface free energy and hence the tendency for coalescence.
23.
24.
25.
26.
27.
28. (a) Flocculation and creaming
(b) Coalescence and breaking
(c) Miscellaneous physical and chemical changes
(d) Phase inversion.
Flocculation
• Neighboring globules come closer to each other and form
colonies in the continuous phase. This aggregation of
globules is not clearly visible.
• This is the initial stage that leads to instability.
• Flocculation of the dispersed phase may take place before,
during or after creaming.
29. • The extent of flocculation of globules depends on
(a) globule size distribution.
(b) charge on the globule surface.
(c) viscosity of the external medium.
(a) Globule size distribution
• Uniform sized globules prevent flocculation.
• This can be achieved by proper size reduction process.
(b) Charge on the globule surface
• A charge on the globules exert repulsive forces with the
neighboring globules.
• This can be achieved by using ionic emulsifying agent,
electrolytes etc.
30. (c) Viscosity of the external medium.
• If the viscosity of the external medium is increased, the
globules become relatively immobile and flocculation can be
prevented.
• This can be obtained by adding viscosity improving agents
(bodying agents or thickening agents) such as hydrocolloids
or waxes.
• Flocs slowly move either upward or downward leading to
creaming.
• Flocculation is due to the interaction of attractive and
repulsive forces, whereas creaming is due to density
differences in the two phases.
31. Creaming
• Creaming is the concentration of globules at the top or
bottom of the emulsion.
• Droplets larger than 1 mm may settle preferentially to the top
or the bottom under gravitational forces.
• Creaming may also be observed on account of the difference
of individual globules (movement rather than flocs).
• It can be observed by a difference in color shade of the layers.
32. • It is a reversible process, i.e., cream can be redispersed easily by
agitation, this is possible because the oil globules are still
surrounded by the protective sheath of the emulsifier.
• Creaming results in a lack of uniformity of drug distribution. This
leads to variable dosage. Therefore, the emulsion should be
shaken thoroughly before use.
• Creaming is of two types, upward creaming and downward
creaming
33. • Upward creaming, is due to the dispersed phase is less dense than
the continuous phase. This is normally observed in o/w emulsions.
The velocity of sedimentation becomes negative.
• Downward creaming occurs if the dispersed phase is heavier
than the continuous phase. Due to gravitational pull, the
globules settle down. This is normally observed in w/o emulsions.
• Since creaming involves the movement of globules in an emulsion,
Stokes’ law can be applied.
ν = d2
(ρs – ρ0)g
18 η0
ν = terminal velocity in cm/sec,
d is the diameter of the particle in cm,
ρs and ρ0 are the densities of the dispersed phase and dispersion medium
respectively,
g is the acceleration due to gravity and
η0 is the viscosity of the dispersion medium in poise.
34. • Creaming is influenced by,
– Globule size
– Viscosity of the dispersion medium
– Difference in the densities of dispersed phase and dispersion medium.
Creaming can be reduced or prevented by:
1. Reducing the particle size by homogenization. Doubling the
diameter of oil globules increases the creaming rate by a factor of
four.
2. Increasing the viscosity of the external phase by adding the
thickening agents such as methyl cellulose tragacanth or sodium
alginate.
35. 3. Reducing the difference in the densities between the dispersed
phase and dispersion medium.
• Adjusting the continuous phase and dispersed phase
densities to the same value should eliminate the tendency to
cream.
• To make densities equal, oil soluble substances such as
bromoform, β-bromonaphthalene are added to the oil phase
(rarely used technique).
36.
37. Coalescence is observed due to:
Insufficient amount of the emulsifying agent.
Altered partitioning of the emulsifying agent.
Incompatibilities between emulsifying agents.
• Phase volume ratio of an emulsion has a secondary
influence on the stability of the product and represents the
relative volume of water to oil in emulsion.
38. • At higher ratio (>74% of oil to water), globules are closely
packed, wherein small globules occupy the void spaces
between bigger globules.
• Thus globules get compressed and become irregular in shape,
which leads to fusion of adjacent globules.
• Ostwald and others have shown that if one attempts to
incorporate more than about 74% of oil in an o/w emulsion, the
oil globules often coalesce and the emulsion breaks.
• This value known as the critical point, is defined as the
concentration of the dispersed phase above which the
emulsifying agent cannot produce a stable emulsion of the
desired type.
39. Breaking
• Separation of the internal phase from the external phase is
called breaking of the emulsion.
• This is indicated by complete separation of oil and aqueous
phases, is an irreversible process, i.e., simple mixing fails. It is
to resuspend the globules into an uniform emulsion.
• In breaking, the protective sheath around the globules is
completely destroyed and oil tends to coalesce.
40. Phase inversion
• This involves the change of emulsion type from o/w to w/o or
vice versa.
• When we intend to prepare one type of emulsion say o/w, and if
the final emulsion turns out to be w/o, it can be termed as a sign
of instability.
