 Combine
two immiscible liquid phases one
of which is dispersed as globules (the
dispersed phase) in the other liquid phase
(the continuous phase) stabilized by
presence of emulsifying agent.
1. They can mask the bitter taste and odor of drugs,
e.g. castor oil, cod-liver oil etc.
2. They can be used to prolong the release of the drug
thereby providing sustained release action.
3. Essential nutrients like carbohydrates, fats and
vitamins can all be emulsified and can be
administered to bed ridden patients as sterile
intravenous emulsions.
4. Emulsions provide protection to drugs which are
susceptible to oxidation or hydrolysis.
6. Emulsions are used widely to formulate externally
used products like lotions, creams, liniments etc.
Based on type:
1- Oil in water emulsions (O/W)
2- Water in oil emulsions (w/O)
3- Multiple emulsions (O/W/O) or (W/O/W)
Based on size of dispherse phase:
1. macroemulsion
2. microemulsion (nanoemulsion)
1. It should be able to reduce the interfacial
tension between the two immiscible liquids.
2. It should be physically and chemically
stable , inert and compatible with the other
ingredients of the formulation.
3. It should be non irritant and non toxic in
the conc., used.
4. It should be able to produce and maintain
the required viscosity of the preparation.
5. It should be able to form a coherent film
around the globules of the dispersed phase
and should prevent the coalescence of the
droplet of the dispersed phase.
1-Natural emulsifying agents
(vegetable source)
acacia - tragacanth- pectin- starch,
derivative of cellulose (semisintetic)
(animal source)
gelatin- cholesterol – lecitin, wool fat
 Advantages: Non toxic and relatively
 Disadvantages:
They show considerable batch to batch variation
readily support M.O. growth
 2-
Finely divided solid:
 Mg(OH)2, bentonite, aluminium
magnesium stearate, attapulgite,
colloidal anhydrous silica and hectorite
 forming
a coherent film which physical
prevents coalescence of the dispersed
 if the particles are: preferntially wetted by
the aqueous phase
o/w emulsion
 preferntially wetted by the oil phase
w/o emulsion
 3-
Synthetic emulsifying agents as:
A- Anionic emulsifying agents
 Alkali soap:
 e.g. sodium, potassium and ammonium salts
of fatty acids
 Form o/w emulsions
 in acidic condition
 incompatible
with polyvalent cations
Soap of di/trivalent metal
 - e.g. Cal oleate
 - Promote w/o emulsions
Amine soaps: N(CH2CH2OH)3
 - neutral pH
 - incompatible with acids and high concentration of
 - Produce o/w emulsion
Sulfated and sulfonated compound
 - E.g.Sodium lauryl sulphate
 - stable over high pH range
 - o/w emulsions
B- Cationic surfactants
 Quaternary ammonium compounds:
 E.g. Cetyl trimethylammonium bromide
(Cetrimide) and benzalkonium chloride
 Toxicity and irritancy
 Incompatible with anionic surfactants,
polyvalent anions
 unstable at high pH
C- Nonionic surfactants
 Low toxicity and irritancy so suitable for oral and
Parenteral administeration
 High degree of compatibility
 Less sensitive to change pH or to addition of
E.g. Tweens (polyethylene fatty acid ester)
Span ( sorbitan fatty acid ester)
glyceryl monostearate, propylene glycol
monostearate, macrogol esters such as
polyoxyl stearates and polyoxyl-castor oil
D- Amphoteric surfactants
 charge depending on the pH of the system
low pH
high pH
 i.e.
lecithin: used to stabilize i.v., fat
 HLB:
the ratio between the hydrophilic
portion of the molecule to the lipophilic
portion of the molecule.
 The higher the HLB of an agent the more
hydrophilic it is.
 Griffin
 HLB = 20 (1 – S / A)
 S: saponification number of the ester
 A: the acid number of the fatty acid
 Davis
 HLB = hydrophilic group number + lipophilic
group number + 7
1. 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)
2. 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
(ii) contact charging (phase with higher
dielectric constant is charged positively)
No correlation between droplet charge and
emulsion stability in W/O emulsions
3. Viscosity of the continuous phase
4. Size distribution of droplets
5. Phase volume ratio
As volume of dispersed phase  stability of
emulsion 
(eventually phase inversion can occur)
6. Temperature
Temperature , usually emulsion stability 
Temp affects – Interfacial tension, solubility
of surfactant, viscosity of liquid, phases of
interfacial film
1. Dilution test
2. Conductivity Test
3. Dye-Solubility Test
4. Fluorescence test
4. Fluorescence test
 oils give fluorescence under UV light, while
water doesn’t. Therefore, O/W emulsion
shows spotty pattern while W/O emulsion
1. Continental or dry gum method
Emulsifier is triturated with the oil in
perfectly dry porcelain mortar
water is added at once triturate
immediately, rapidly and continuously (until
get a clicking sound and thick white cream is
formed, this is primary emulsion)
the remaining quantity of water is slowly
added to form the final emulsion
2. English or Wet Gum Method
triturate gum with water in a mortar to form a
oil is added slowly in portions the mixture is
after adding all of the oil, thoroughly mixed for
several minute to form the primary emulsion
Once the primary emulsion has been formed
remaining quantity of water is added to make
the final emulsion
3. Bottle or Forbes Bottle Method
It is extemporaneous preparation for volatile oils
or oil with low viscosity.
gum + oil (dry bottle)
water (volume equal to oil) is added in portions
with vigorous shaking to form primary emulsion
remaining quantity of water is added to make
the final emulsion
a) Flocculation and creaming
 Creaming related to stokes equations
 Explain its!!
 The solution is…..
b) coalescence and breaking/cracking
c) Phase inversion
d) Miscellaneous physical and chemical
It may be brought about by:
 1- the addition of an electrolyte e.g.
addition of CaCl2 into o/w emulsion formed
by sodium stearate can be inverted to w/o.
 2- by changing the phase volume ratio
 3- by temperature changes.
Phase inversion can be minimized by:
 1- using the proper emulsifying agent in
adequate concentration
 2- keeping the concentration of dispersed
phase between 30 to 60 %
 3- storing the emulsion in a cool place
 Cracking
of emulsion can be due to:
 1- addition of an incompatible emulsifying
agent , e.g. monovalent soap + divalent soap
e.g. anionic + cationic emulsifying agent
2- chemical or microbial decomposition of
emulsifying agent
 e.g. alkali soaps decomposed by acids
 e.g. monovalent soaps salted out by
electrolytes such as NaCl
 e.g. nonionic emulsifying agents are
incompatible with phenols
 e.g. alcohol precipitates gums and gelatin
 3-
exposure to increased or reduced
 4- Addition of common solvent
 e.g. addition of a solvent in which the two
phases are soluble (alcohol)
 Contamination
due to microorganisms can
result in problems such as:
 1- color and odor change
 2- gas production
 3- hydrolysis
 4- pH change
 5- breaking of emulsion
1. Determination of
2. Determination of
3. Determination of
4. Determination of
particle size and particle
phase separation: