In this presentation Theories of dispersion, pharmaceutical dispersion (Emulsion and suspension) with their mechanism, methods of preparation and stability studies are mentioned.

1. THEORIES OF DISPERSION,
PHARMACEUTICAL DISPERSION
(EMULSION AND SUSPENSION)
By-
Dipesh Adesh Gamare

2. Theories of dispersion, pharmaceutical dispersion (Emulsion and
suspension) and SMEDDS
 Pharmaceutical dispersion.
 Theories of dispersion : a) Viscosity theory
b) Film theory or adsorption theory
c) Wedge theory
d) Interfacial tension theory
 Emulsion- Definition, Mechanism of emulsification, Method of preparation
and stability of emulsion.
 Suspension- Definition, Mechanism, Method of preparation and stability of
suspension.

3. Pharmaceutical dispersion
 Dispersed system consists of particulate matter, known as the dispersed
phase, distributed throughout continuous or dispersion medium.
 The dispersed material may range in size from particles of atomic and
molecular dimensions to particle whose size is measured in millimeters.
COARSE DISPERSION SYSTEM
Emulsion
Colloids
Suspension

4. Theories of dispersion
a) Viscosity theory
• As per this theory increase in viscosity of emulsion will leads to increase
in stability of it.
 Limitations
• This theory fails to explain the viscosity related to milk, as milk don’t
possess viscous nature but still it shows the good stability.

5. b) Film theory or adsorption theory
• As per this theory, the added emulsifying agent forms a mechanical film
by getting adsorbed at the interface of the liquids (i.e. at the interface
between the dispersed globules and the dispersion medium).
• This offers stability to the emulsion.
 Limitations
• This theory could not explain the formation of type of emulsion.

6. c) Wedge theory
• According to this theory, monovalent soaps Iike sodium stearate gives o/w type
emulsion and divalent soaps like calcium stearate gives w/o type emulsion.
• This was explained by the successful accommodation of the soap molecules at the
interface and subsequent possible orientation of the soap molecules to give the type
of emulsion
 Limitations
• This theory could not explain the formation of type of emulsion.
• The calcium stearate will not obey this theory, it will ionize and will not exist as a
wedge.

7. d) Interfacial tension theory
 Initially when the oil and water are mixed together, they will become
immiscible due to the interfacial tension formed between surface of oil
and water.
 The added emulsifying agent reduces the interfacial tension between the
oil and the water phase by emulsifying the mixture.
 Hence a stable emulsion is formed.

8. EMULSIONS
 An emulsion is a biphasic liquid preparation containing two immiscible
liquids, one of which is dispersed as minute globules into the other.
 The liquid which is converted into minute globules is called the
'dispersed phase' and the liquid in which the globules are dispersed is
called the 'continuous phase'.
 Normally, two immiscible liquids cannot be dispersed for a long period.
 So, an emulsifying agent is added to the system.
 It forms a film around the globules in order to scatter them indefinitely in
the continuous phase, so that a stable emulsion is formed.
 The globule size in emulsion varies from 0.25 to 25 μm.

9. HLB (Hydrophilic lipophilic balance) values of emulsifying
agents

10. Mechanism of emulsification
 When two immiscible liquids are in contact with each other, the
molecules at the interface experiences a perpendicular force.
 The net forces at the interface are called as interfacial tension and tend
to minimize the surface are of individual liquids.
 In emulsion, the process of dispersion of one liquid in the other results
in an increase in the surface area between the dispersed droplets and
dispersion medium, and surface free energy, which can be expressed
as follows :
 ΔW = g Δ A
Where ΔW = increase in the free energy at the interface
Δ A = increase in the surface area

11. Methods of preparation of emulsion
 Commercially, emulsions are prepared in large volume mixing tanks and
refined and stabilized by passage through a colloid mill or homogenizer.
Extemporaneous production is more concerned with small scale
methods.
 Methods of preparation:
A. Dry gum method
B. Wet gum method
C. Bottle method
D. Beaker method
E. In-situ soap method

12.  Dry gum method is used to prepare the initial or primary emulsion from oil, water, and a hydrocolloid or
"gum" type emulsifier.
 Dry Gum Methodology includes (4 parts oil,2 parts water, and ,1 part of emulsifier).
Procedure:
 Take mortar, 1 part gum is levigated with tile 4 parts oil until the powder is thoroughly wetted; then the
2 parts water are added all at once, and the mixture is vigorously triturated until the primary emulsion
formed is creamy white and produces a clicking sound as it is triturated.
 Active ingredients, preservatives, color, flavors are added as a solution to the primary emulsion.
 When all agents have been incorporated, the emulsion should be transferred to a calibrated vessel,
brought to final volume makeup by water.
A) Dry Gum Method

13.  Methodology
(Oil 4 parts + Water 2 parts + Emulsifier 1parts)
Procedure:
 In this method, the proportions of oil, water, and emulsifier are the same (4:2:1), but
the order and techniques of mixing are different.
 The 1 part of gum is triturated with 2 parts of water to form a mucilage; while
triturating add 4parts oil is slowly.
 After all the oil is added, the mixture Is triturated for several minutes to form the
primary emulsion.
 Then other ingredients may be added as in the continental method.
B) Wet Gum Method

14.  This method may be used to prepare emulsions of volatile oils, oleaginous
substances of very low viscosities. This method Is a variation of the dry gum method.
Procedure:
 One-part powdered acacia (or other gum)ls placed in a dry bottle and four parts oil
are added.
 The bottle is capped and thoroughly shaken.
 To this, the required volume of water is added all at once, and the mixture ls shaken
thoroughly until the primary emulsion forms.
C) Bottle Method

15.  Dividing components into water soluble and oil soluble components.
 All oil soluble components are dissolved in the oily phase in one beaker and all
water-soluble components are dissolved in the water in a separate beaker
Procedure:
 Oleaginous components are melted and both phases are heated to approximately
70*C over a water bath.
 The Internal phase is later added to the external phase with stirring until the product
reaches room temperature.
D) Beaker method

16. Two types of Soaps developed by this Methods
 Calcium Soaps
 Soft Soaps
Procedure:
1) Calcium Soaps: W/O type Emulsions.
 E.g., Oleic acid + lime water.
 Prepared by simple mixing of equal volumes of oil and lime water.
 Calcium salts of free fatty acids is used as emulsifying agent.
 Example : Olive Oil + Oleic acid
E) In-situ soap method

17. Stability of emulsion

18. Stability of emulsion

19. Suspension
 Suspension are the biphasic liquid dosage form of medicament in
which the finely divided solid particles ranging from 0.5 to 5.0 micron
are dispersed in a liquid or semisolid vehicle.
 The solid particles act as disperse phase whereas liquid vehicle acts
as the continuous phase.
 Suspension are generally taken orally or by parenteral route.
 They are also used for external applications

20. Mechanism of suspension formation
 A Pharmaceutical suspension is a coarse dispersion in which internal
phase (therapeutically active ingredient)is dispersed uniformly
throughout the external phase, maintained uniformty through out the
suspending vehicle with aid of single or combination of suspending
agent.
 Suspending agent is a kind of viscous hydrophilic colloidal substance,
which can increase the viscosity of the dispersion medium to slow down
the sedimentation speed of particles and adsorb on the surface of the
particles to become a barrier to prevent the aggregation and
agglomeration of particles.

21. Method of preparation
Suspension can be prepared by 2 methods :
1) Dispersion method
2) Precipitation method: a) Organic solvent precipitation
b) Precipitation effected by changing pH of the medium
c) Double decomposition

22. 1)Dispersion method
Solid phase is wetted and dispersed
Use of surfactant to ensure wetting of
hydrophobic solids
Vehicle is formulated

23. Dissolve in organic solvent
a) Organic solvent precipitation
Add organic phase to water
- Organic solvents include
ethanol, methanol, propylene
glycol and polyethylene
glycol
Water insoluble drugs
b) Precipitation effected by changing
pH of the medium
Concentrated solution in favorable pH.
Pour to other system to change pH
Applicable to those drugs whose
solubility is dependent on pH.
On agitation precipitate will form
e.g. estradiol suspension.
c) Double decomposition
Zinc sulphate solution
Two water soluble reagents forms a water
insoluble products. e.g. White lotion NF
Solution of sulphurated potash
Precipitate of zinc polysulphide
2) Precipitation method

24. Stability of suspensions
1) Small particle size
 Reduction in the size of the dispersed particle increase the total surface area
of the solid. The greater the degree the subdivision of a given solid the larger
the surface area.
 The Increase in surface area leading to increase in viscosity of a system.
2) Temperature
 Another factor which negatively affects the stability and usefulness of
pharmaceutical suspensions is fluctuation of temperature.
 Temperature fluctuations can lead caking of claying.

25. 3) Increasing the viscosity
 Increasing the viscosity of the continuous phase can lead to the stability of
suspension, this happens because the rate or sedimentation can be reduce by
increase in viscosity.
 Viscosity increase is brought about by addition of thickening agents to the external
phase and they must be soluble or swell in water.
 It is important to note that the rate or release of a drug from a suspension also
dependent on viscosity of a product.
 The more viscous the preparation, the slower is the release of a drug and this
sometimes give desirable for depot preparations.

26. References
1.Leon lachmann, Herbert A. lieberman. The Theory & Practice of Industrial
Pharmacy. 2009 Edition.
2.Textbook of Physical Pharmacy by Alfred Martin, Varghese publication.
3.Textbook of Modern Pharmaceutics by Gilbert & Banker.
4.Textbook of pharmaceutical practice by M .Alton pharmaceutical dosage forms.
5.pharmaceutical pre-formulation by J.T.Carstensen, Ph.D