theories of dispersion

1. Theories Of Dispersion
And Pharmaceutical
Dispersion
Presented BY:
Abhishek Chauhan
M.Pharm 1st year
Dept.of Pharmaceutics
ISFCP,Punjab
Facilitated To:
Mr. Balak Das Kurmi
Dept. of Pharmaceutics
ISFCP,Punjab

2. contents:
Theories of Dispersion
Emulsion Definition
Method of Preperation of Emulsion
And Stability
Suspension Definition
Preperation of Suspension And
Stability

3. 4.Interfacial tension theory
:
There are mainly 4 theories
1.Viscousity theory
2. Film Theory or adsorption theory
3.Wedge Theory

4. . LIMITATIONS OF THE THEORY
1.VISCOUSITY THEORY
As per this theory, an increase in viscosity of emulsion will lead
to an increase in stability
This theory failed to explain about the milk, which shows
considerable stability even though its viscosity is less.

5. LIMITATIONS
2.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
This theory could not explain the formation of type of emulsion

6. According to this theory, monovalent soaps like sodium sterate
gives o/w type emulsion and divalent soaps like calcium sterate
gives w/o type emulsion.
The calcium sterate will not obey this theory, it will ionize and
will not exist as a wedge.
3.WEDGE THEORY
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 .
This theory could not explain the stability of an emulsion.
. LIMITATIONS

7. . Hence a stable emulsion is formed.
4.INTERFACIAL TENSION THEORY
Initially when the oil and water are mixed together, they will
become immiscible due to the interfacial tension.
The added emulsifying agent reduces the interfacial tension
between the oil and the water phase.

8. Where as the dispersed medium is known as the external or
continuous phase.
Emulsion:
A thermodynamically unstable system consisting of at least 2
immiscible liquid phases, 1 of which is dispersed as globules in
the other liquid phase.
.The dispersed liquid is known as the internal or discontinuous
phase.

9. 5.In situ Soap Method
Methods of Preparation Of Emulsions
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:
1.Dry Gum Method 2.Wet Gum Method
3.Bottle Method 4.Beaker Method

10. When all agents have been incorporated, the emulsion should
be transferred to a calibrated vessel, brought to final volume
with water.
1.DRY GUM Method:
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 (4 parts oil, 2 parts water, and 1 part
Emulsifier).
Procedure:
Take mortar, 1 part gum is levigated with the 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
"cliking" sound as it is triturated.
Active ingredients, preservatives, colour, flavours are added as a solution
to the primary emulsion.

11. .Then other ingredients may be added as in the continental
method.
2.Wet Gum Method:
: Methodology
(Oil 4 parts + Water 2 parts + Emulsifier 1 parts)
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 gum is triturated with 2 parts water to form a
mucilage; then the 4 parts oil is added slowly, in portions, while
triturating
After all the oil is added, the mixture is triturated for several
minutes to form the primary emulsion.

12. To this, the required volume of water is added all at once, and
the mixture is shaken thoroughly until the primary emulsion
forms.
3.Bottle Method:
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.
One part powdered acacia (or other gum) is placed in a dry
bottle and four parts oil are added.
The bottle is capped and thoroughly shaken.

13. The internal phase is then added to the external phase with
stirring until the product reaches room temperature.
4.Beaker Method:
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
Oleaginous components are melted and both phases are
heated to approximately 70°C over a water bath.

14. 5.In situ Soap Method:
Two types of Soaps developed by this Methods
Calcium Soaps
Soft Soaps
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.
Emulsifying agent used is Calcium salt of free fatty acids.
E.g. Olive Oil + Oleic acid

15. Instability in Emulsion:
Instability Factors
1) Uniform globule size distribution.
2) Opposite charge on globule surface.
3) Low viscosity of external medium.
1) Globul size.
2) Viscosity of external medium.
3) Differences in density of oil-water
(aq>oil)
1. Insufficient amount of E.A
2. Altered partitioning of E.A
3. Incompatibility between E.A
Preventions
1) Uniform sized globules.
2) Use same charged ionic electrolytes.
3) Viscosity improving agents
hydrocolloids.
NO this is permanent change
Floculations:Globules
come closes to each other
to form aggregates.
Creaming:
Concentration of globules
at top/bottom of
emulsion.
Coalescence:
Few globules fuse to form
bigger globules emulsifier
film is destroyed.
1. Homogenization uniformed sized
globules.
2. 2. Thickening agents to improve
viscosity.
3. 3. Reducing density differences
(Bromoform+oil).

16. Suspension:
A pharmaceutical suspension is a coarse dispersion in which
internal phase is dispersed uniformly throughout the external
phase.
Method of Preparation of suspension:
Suspension can be prepared by 2 methods :
Dispersion method
Precipitation methods
: Precipitation methods:
Double decomposition
Three main methods
Organic solvent precipitation
Precipitation effected by changing pH of the medium

17. Organic solvent precipitation:
Water insoluble drugs
Dissolve in organic solvent
Add organic phase to water
organic solvent include
ethanol,methanol,propylene glycol and
polyethylene glycol.

18. Precipitation effected by changing pH of the medium:
Applicable to those drugs in which solubility is
dependent on ph value.
Concentrated solution in favourable ph
Pour to other system to change ph
On agitation precipitate will form
e.g. estradiol suspension.

19. Double decomposition:
Two water soluble reagents forms a water insoluble products.
e.g. white lotion NF
Zinc sulphate solution
Solution of sulphurated potash
Precipitate of zinc polysulphide

20. 2.Dispersion method:
Vehicle is formulated
solid phase is wetted and dispersed
use of surfactant to ensure wetting of
hydrophobic solids.

21. Stability of suspension:
The increase in surface area means also an liquids leading to
an increase in viscosity of a system.
1)Small particle size:
Reduce 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.
Temperature fluctuations can lead caking of claying.
2) Temperature:
Another factor which negatively affects the stability and
usefulness of pharmaceutical suspensions is fluctuation of
temp.

22. The more viscous the preparation, the slower Is likely to be the
release of a drug sometimes this property may be desirable for
depot preparations.
3.Increasing the viscosity:
Increasing the viscosity of the continuous phase can lead to the
stability of suspension this is so because the rate of
sedimentation can be reduce by increase in viscosity.
Viscosity increase is brought about by addition of thickening
agents to the external phase. In water these must be either
soluble or swell.
It is important to note that the rate of release of a drug from a
suspension is also dependent on viscosity of a product.

23. 5. Pharmaceutical preformulation by J.T.Carstensen, Ph.D
. REFERENCE
1. Leon Lachmann,HerbertA. Lieberman. The Theory & Practice
of Industrial Pharmacy. 2009 Edition
2. Text book of Physical Pharmacy by Alfred Martin, Varghese
publication
3. Text book of Modern Pharmaceutics by Gilbert &Banker
4. Text book of pharmaceutical practice by M .Alton. pharmaceutical dosage forms

24. THANK YOU