Emulsion

COARSE DISPERSIONS:
EMULSION
Dr. Y.Ramesh M. Pharm., Ph. D
Department of Pharmaceutics
Associate Professor
Ratnam Institute of Pharmacy
Pidathapolur (V), Muthukur (M)
S.P.S.R. Nellore

CONTENTS
Definition
Classification
Types of Emulsion
Detection test
Mechanism of action
Theories of emulsifying agents
Instability
Application
Storage and Packing
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NELLORE

Definition: The word "emulsion" comes from
the Latin word for "to milk“.
EMULSION: An emulsion is a mixture of two
or more liquids that are normally
immiscible (nonmixable or unblendable).
OR
Definition: An emulsion is a thermodynamically
unstable system containing mixture of two or
more immiscible liquids which is stabilized
by adding emulsifying agent
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INTRODUCTION
Emulsions are part of a more general class of
two-phase systems of matter called colloids.
Emulsion should be used when both the
dispersed and the
continuous phase are liquids.
Examples of emulsions include vinaigrettes,
milk, mayonnaise, and some cutting fluids for
metal working. The photo-sensitive side of
photographic film is an example of a colloid.
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CLASSIFICATION OF EMULSION
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TYPES OF EMULSION
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DIFFERENCE BETWEEN O/W & W/O
TYPE OF EMULSION
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DETECTION TEST
• Dilution Test: Based on the solubility of
external phase of emulsion.
• o/w emulsion can be diluted with water.
• w/o emulsion can be diluted with oil.
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Conductivity test: Water is good conductor of
electricity where as oil is non conductor. There
continuous phase of water runs electricity
more than continuous phase of oil.
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Dye-solubility test: When an emulsion is
mixed with a water soluble dye such as
amaranth and observed under the
microscope. If the continuous phase
appears red, then it means that emulsion is
o/w type as water is the external phase if
the scattered globules appear red and
continuous phase colorless, then it is w/o
type.
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Fluorescence Test: Oil give Fluorescence under UV light,
while water doest not. There o/w emulsion shows
spotty pattern while w/o emulsion fluoresces.
Applications of Emulsion
• Oral administration of water insoluble liquids (Fat
soluble vitamins).
• Intravenous administration of API as an emulsion (e.g.
Taxol)
• Emulsions for external use (e.g. Lotions, liniments)
• Emulsions in aerosol can be used to produce foam.
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Theories of emulsification
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Theories of emulsification
1) Surfactant (Monomolecular asorption): To reduce
the interfacial tension oil droplets are surrounded by
a coherent monolayer of the surfactant whivh
prevents coalescence. If the emulsifier is ionized the
presence of strong charge may lead to repulsion in
droplets and hence increasing stability.
2) Hydrophilic colloids (multimolecular adsorption)
3) Finely divided solid particles (solid particles
adsorption): They are adsorbed at the intertface
between two immiscible liquid phass to form
particulate film.
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Emulsifying agents
(Mechanism of action)
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Monomolecular adsorption: Amphiphiles
(surfactants Amphiphiles (surfactants) reduce
interfacial tension (to 1 dyne/cm) because of
adsorption at interface o/w Droplets are
sorrounded by coherent monolayer that help
prevent coalesence (merging) between two
droplets Surface Charge cause repulsion
between globules
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Combination of surfactants is generally
used as it is more effective Combinnation
of Sodium cetyl sulphate and cholestrol
leads to complex film that produce
excelent emulsion Hydrophilic Tween
can be combined with Lipophilic Span,
varying proportions produce desired
emulsion... w/o or o/w
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Surfactant / co-surfactant
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Monomolecular Adsorption
(HLB)
Type of emulsion produce depend on property of
emulsifying agents. Hydrophilic lipophilic
balance (HLB). Type of emulsion is function
of relative solubility of the surfactant.
Rule of Bancroft: The phase (oil/water) in which
surfactant is relatively more soluble will
become continuous phase. High HLB
Surfactant prefer formation o/w emulsion and
vice versa.
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HLB: A system was developed to assist
in making systemic decisions about
the amounts and types of surfactants
needed in stable products. The system
is called the HLB (hydrophile
lipophile balance) system and has an
arbitrary scale of 1 - 18. HLB numbers
are experimentally determined for the
different emulsifiers.
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Anionic surfactants:
These are organic salts which, in water, have a surface-active
anion. E.g. Alkali metal and ammonium soaps (salts of long
chain fatty acids) such
as sodium stearate and potassium oleate (o/w).
✓ Soaps of divalent and trivalent metals such as calcium oleate
(w/o).
✓ Amine and ammonium soaps such as triethanolamine oleate
(o/w).
✓ Alkyl sulphates such as sodium lauryl sulphate (SLS) (o/w).
Disadvantages:
They are irritant internally so widely used in external
preparations as o/w emulsifying agents.
Anionic surfactants are generally stable at more alkaline pH
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Cationic surfactants: These are usually quaternary
ammonium compounds. which have a surface-active
cation. Examples include cetrimide and
benzalkonium chloride. They are used in the
preparation of o/w emulsions for external use and
must be in their ionized form to be effective. The
cationic surfactants also have antimicrobial activity.
Disadvantages:
1. Emulsifying agents (Surfactants Examples)
2. They are sensitive to anionic surfactants and drugs.
3. Emulsions formed by a cationic surfactant are
generally stable at acidic pH.
4. They are more toxic than other surfactants.
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Multimolecular Adsorption (Hydrocolloids)
Hydrophilic colloids (mucilage of gum acacia)
are different in action from surfactants.
They do not cause lowering of interfacial tension
They form multimolecular layer at o/w interface,
action of hydrocolloids is because of this
reason.
They increase viscosity of dispersion medium.
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Natural Polysaccharides: The main problem with
these agents is their natural variability between
batches and microbial contamination. These materials
should not be used externally as they leave a sticky
feel on the skin.
Acacia is the best emulsifying agent for
extemporaneously prepared oral emulsions as it
forms a thick film at the oil water interface to act as a
barrier to coalescence. It is too sticky for external use.
Tragacanth is used to increase the viscosity of an
emulsion and prevent creaming. Other
polysaccharides, such as starch, pectin and
carrageenan, are used to stabilize an emulsion.
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Semi-synthetic polysaccharides: These are derived
from the naturally occurring polysaccharide cellulose
and generally form o/w emulsions.
Examples include low-viscosity grades of
✓Methylcellulose (MC)
✓Carboxymethylcellulose (CMC)
✓Hydroxypropylmethylcellulose (HPMC)
Synthetic hydrocolloids:
✓Carbopol
✓Polyvinyl alcohol (PVA).
✓Polyvinyl pyrolidone (PVP)
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3) Solid Particles Adsorption: Solid
particles that can be wetted by oil as
well as water can act as emulsifying
agent. Their concentration is higher
at interface. They form particulate
film around dispersed droplets to
prevent coalescence. Example of
agents: Bentonite, Aluminum
Silicate)
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EMULSION INSTABILITY
The instability of pharmaceutical emulsions
may be classified as following:
Flocculation and creaming
Coalescence and breaking
Phase inversion
Miscellaneous physical and chemical
change
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FLOCCULATION: The small
spheres of oil join together to form
clumps or flocks which rise or settle
in the emulsion more rapidly than
individual particles.
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CREAMING: It is the concentration of the floccules of
the internal phase form upward or downward layer
according to the density of internal phase.
CREAMING: Stokes equation included the factors
that
affect the creaming process:
dx/dt=d2 (pi-pe)g/18n
dx/dt=rate of setting
D=diameter particle
p=density of internal phase and external phase
g=gravitational constant
n=viscosity of medium
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Factors affect creaming:
Globule size: ↑globule size ↑creaming
The density of the internal phase and
External phases:
pi-pe=0 dx/dt=0
pi-pe=-ve [i.e.-ve velocity upward creaming]
pi-pe=+ve [downward creaming]
Gravity: Constant, however centrifugation is
applied
Velocity: ↑ ↓creaming
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COALESCENCE: It is the process by
which emulsified particles merge
with each to form large particles.
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BREAKING: Due to coalescence and
creaming combined, the oil separates
completely from water so that it
floats at the top in a single,
continuous layer.
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DIFFERENCE BETWEEN
CREAMING AND CRACKING
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PHASE INVERSION: In phase inversion o/w type emulsions
changes into w/o type and vice versa. It is a physical
instability.
It may be brought about by: the addition of an electrolyte e.g.
addition of calcium chloride into o/w emulsion formed by
sodium stearate can be inverted to w/o. by changing the phase
volume ratio. by temperature changes.
Phase inversion can be minimized by: By using the proper
emulsified agent in adequate concentration. keeping the
concentration of dispersed phase between 30 to 60%. storing
the emulsion in a cool place.
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CRACKING: When an emulsion
cracks during preparation. i.e the
primary emulsion does not become
white but acquires an oily translucent
appearance. In such a case it is
impossible to dilute the emulsion
nucleus with water and the oil
separates out.
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Cracking of emulsion can be due to:
1. Addition of an incompatible emulsifying
agent: e.g. monovalentsoap + divalent
soap
2. Chemical or microbial decomposition of
emulsifying agent:
e.g. alkali soap decompose by acid.
3. Exposure to increased or reduced
temperature
4. Addition of common solvent.6/25/2020 46
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Pharmaceutical Application:
It covers the unpleasent taste
Increase absorptin rate.
Topical emuslions are washable.
Having acceptable viscosity.
Less greasy.
Controlled drug release.
Increased Bioavailability.
Protection of thermolibile drugs.
Reduce Patients Variability.
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STORAGE & PACKING
Depending on the use, emulsions should be packed in suitable
containers. for oral use, usually packed in well filled bottles
having an air tight closure.
Light sensitive products: Packed in amber colored bottles.
For viscous emulsions: Wide mouth bottles should be used.
The label on the emulsion should mention that these products
have to be shaken thoroughly before use. External use products
should clearly mention on their label that they are meant for
external use only.
Emulsions should be stored in a cool place but refrigeration
should be avoided as this low temperature can adversely effect
the stability of preparation.
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