EMULSIONS
Emulsion is a biphasic liquid
preparation containing two immiscible liquids one of which is dispersed as
minute globules into the other with the help of an emulsifying agent.
The liquid that is broken up into
globules is called dispersed phase & the liquid in which the globules are
dispersed in known as continuous phase.
Types of emulsion:
They are two types
1. Oil in water:
In
O/w type, oil is dispersed phase & water is continuous phase. In oil in
water type, oil is surrounded by water. So the un-pleasant taste & odour of
the oil is masked. Therefore o/w type of emulsion is preferable for internal
use.
2.
Water in oil type:
In
w/o type water is the dispersed
phase & oil is in the continuous phase. In w/o type, water is surrounded by
oil. So application on the skin may be easier. Therefore w/o type of emulsion
preferable for external use.
Different tests for the identification
of emulsion type.
|
o/w |
|
|
1. Dilution test: 2. Dye test: 3. Electrical conductivity test: 4. fluorescence test: |
1. If water is added to w/o type the 2. 3. 4. |
example
for natural emulsion:
Milk is an example for o/w emulsion.
Butter is an example for w/o emulsion.
Emulsifying agent/ surfactants
Surfactants are materials get adsorbed
at the interface between the two phases. The surface adsorption lowers or
decreases the tension between the two phases. It causes the inter mix of the
phases with each other. Hence to reduce surface tension surfactants are used.
They are classified as follows:
1. Natural Emulgents from vegetable sources: These are anionic in nature & produce o/w type emulsions. They
act as primary emulgents & stabilizers. Ex: acacia, tragacanth, agar, pectin
2. Natural emulsifying agents from animal
sources:
a) Gelatin: It occurs in two forms
Pharmagol A- used in acidic PH
Pharmagol B-used in alkaline PH
b) Egg Yolk
c) Wool Fat
3. Semi synthetic polysaccharides: These produce o/w type of emulsion
Ex: Methyl cellulose, sodium CMC
4. Synthetic Emulgents:
a) Anionic: Its anionic part is
responsible for emulsifying activity.
Ex:
– Soaps & sodium lauryl sulphate
b) Cationic: Its cationic part is
responsible for emulsification.
Ex:
– Cetrimide, Benzalkonium chloride.
They produce o/w type emulsion.
c) Non-Ionic: They do not ionize in
aqueous solution. These are stable at wide range of pH & are not affected by addition of acids &
electrolytes.
5. In-organic Emulgents: Ex: – Milk of magnesia, magnesium oxide, magnesium aluminium
silicate & bentonite.
6.
Alcohols: Ex: – Cetyl alcohol, stearyl alcohol,
glycerol mono- stearate. Carbo waxes.
Methods of preparation of emulsions
I. Small scale method:
In
small scale method, stable emulsions are prepared by 3 methods. They are
a) Dry gum method: It involve the following steps
1.
The mortor &
pestle should be absolutely dry.
2.
Measure the
required quantity of oil in a clean measuring cylinder & transfer it into a
dry motor.
3.
Add the
calculated amount of gum acacia to the mortor.
4.
The gum (1 part)
is triturated with oil (4parts) in a dry motor thoroughly to form a uniform
mixture.
5.
Add required
quantity of water (2parts) and triturate till clicking sound is produced &
the product becomes white. This indicates the formation of emulsion, called
primary emulsion.
6.
If any solid
ingredients are present in the formation. They should be dissolved in small
portion of water.
7.
If any other
soluble ingredients are to be added it must be incorporated after making
primary emulsion.
8.
Then more water
is added to produce the required value.
|
Type of oil |
Primary emulsion formula |
||
|
Oil |
Water |
Gum |
|
|
1. fixed oils ex: – Arachis oil castor oil |
4 |
2 |
1 |
|
2. Mineral oil Ex: – Liquid Paraffin |
3 |
2 |
1 |
|
3. Volatile oil Ex: – Turpentine oil cinnamon oil |
2 |
2 |
1 |
|
4. Oleo – resin Ex: – male fern extract, balsam of |
1 |
2 |
1 |
2. Wet gum method: –
The
proportion of oil, gum, water is same as dry gum method for primary emulsion.
The method of preparation of primary emulsion is similar to dry gum method but
it a slower technical. But it gives better result than dry gum method. It is as
follows.
1.
Calculated
quantity of gum acacia is triturated with required quantity of water form a
mucilage.
2.
To this, add oil
in small portions with rapid triturating until the product becomes white &
clicking sound is produced. I.e the formation of primary emulsion.
3.
If any solid
ingredients are present in the formation. They should be dissolved small
portion of water.
4.
If any should
ingredients is to be added it must be incorporated after make primary emulsion.
5.
The more water is
added to produce the required volume.
3. Bottle method:
1.
In this method,
oil is taken in a large bottle and then powdered dry gum is added.
2.
The bottle is
shaken vigorously until the oil and gum are mixed thoroughly.
3.
Then the
calculated amount of water is added all at once and the bottle is shaken
vigorously until primary emulsion is formed.
4.
If any solid
ingredients are present in the formulation, they should be dissolved in small
portion of water.
5.
This solution and
other liquids are added to the primary emulsion and shaken thoroughly. Then
more water is added to produce the required volume.
II) Large scale method:
In
large scale method, stable emulsions are prepared by using homogeniser &
colloidal mill.
H.L.B. scale and its application.
1.
H.L.B means
Hydrophilic – Lipophyllic balance.
2.
It is used for
the selection of emulsifying agent for the preparation of emulsion.
3.
It made balance
between the hydrophilic & Lipophyllic portion of the emulgent.
4.
As the
emulsifying becomes more hydrophilic, its solubility in water increases &
the formation of an o/w type emulsion.
5.
As the emulsifier
becomes more Lipophyllic , its solubility increased & the formation of an
w/o type emulsion.
6.
The H.L.B Scale
is a numerical scale extending from 1-20.
7.
A number is given
to the emulgent depending on the strength of the hydrophilic, lipophyllic
segment of the molecule.
8.
The system mostly
used for non-ionic emulgents.
9.
Emulsifying agents with the higher H.L.B
numbers produce o/w emulsion & lower numbers produce w/o type emulsions.
10. Emulsifying agents with 3-6 value produce w/o emulsion &
emulsifying agents with 8-18 value produce o/w type emulsion.
Application:
The
following are the H.L.B values of few important emulsifying agents.
Ranges Application
1-3 Antifoaming
agents
3-6 Emulsifying
agents (w/o type)
7-9 Wetting agents
8-18 Emulsifying agents
(o/w type)
13-18 Detergent
15-18 solubilising agents
Stability of Emulsions:
Stability:
A formulated emulsion should retain its
original characters like size of the emulsion and their uniform distribution
throughout the contiuous phas
The following are some of the symptoms
of instability of emulsions:
1. Creaming:
Creaming is defined as the upward
movement of the dispersed phase towards the surface and form a thick layer at
the surface of the emulsion.
Reason
for creaming:
1. The size of globules.
2. The viscosity of continuous
phase.
3. The difference between the
densities of the dispersed phase and continuous phase.
4. The temperature.
To
prevent creaming:
1. By reducing size of globules
2. By increasing the viscosity if continuous
phase
3. By reducing the difference between the
densities of the dispersed phase and continuous phase.
4. By storing the emulsion in a cool place.
2. Sedimentation:
Definition: It is defined as the downward movement of the dispersed phase
towards the bottom & form a separate layer over the sedimented particles.
Reasons
for sedimentation:
1.
The size of the globules
2.
The difference between the densities of the dispersed phase & continuous
phase.
Prevention:
Sedimentation can be reduced by the following
ways.
1. By reducing the size of the
globules.
2. By reducing the difference between
the densities of dispersed phase & continuous phase.
3. Cracking:
Cracking can be defined as the
separation of the dispersed phase and continuous phase as two separate layers. They cannot
be re-dispersed on shaking.
Cracking may be caused by physical or
chemical or microbial effects. They change the nature of the emulsifying agent
& reduce the emulsifying property.
Factors effecting the cracking of emulsions:
i)
Chemical factors:
Decomposition or precipitation of
emulsifying agents.
a) Acids:
Acids decompose alkali soaps & the emulsion separate into two phases
b) Electrolytes: Electrolytes
like sodium chloride precipitate the sodium soap & the emulsion separates
into two phases.
c) Alcohols: Alcohol
precipitates the gum & the protein emulsifying agent. The emulsion is
separated into two phases.
ii) Physical
factors:
a) Addition of opposite type of emulsifying
agent emulsifying agent: By adding of o/w
type of emulsifying agent to a w/o type of emulsion, the emulsion separates
into two phases. Ex: Agitation of soft to a calcium
soap emulsion.
b) Addition of common solvent: Addition of solvent in which both dispersed phase & the
continuous phase are soluble. The emulsion from the phase system & destroy
the emulsion. Ex: Addition of alcohol to turpentine
oil, for soft soap emulsion.
c)
Addition of excess dispersed phase:
If the dispersed phase is incorporated to the emulsion the dispersed globules
coagulate & the emulsion separates into two phases.
Ex:
Addition of turpentine oil to the turpentine oil soft soap emulsion.
d) By increasing the temperature: If increase in temperature the viscosity of the emulsion will be
decreased & causes creaming. The creaming is more liable to crack the
emulsion.
iii). Microbial factor:
If the emulsion is not used
immediately & does not contain preservative. There may be growth of mould
& bacteria in the emulsion. It destroys the emulsifying agent. It causes
separation of emulsion into two phases.
4. Phase inversion:
Change of phase that is o/w type of emulsion changes into w/o type of emulsion
and vice versa is known as phase inversion.
Reason
for phase inversion:
1. By the addition of electrolyte.
2. By changing the phase volume ratio
3. By temperature changes.
To
minimise phase inversion:
1. By using the proper emulsifying agent in sufficient concentration.
2. By keeping the concentration of dispersed phase between 30 to 60
percent.
3. By storing the emulsion in a cool place.
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