This document provides an overview of disperse systems, including emulsions and suspensions. It discusses key concepts such as interfacial phenomena, wetting, adsorption, surfactants, and micelle formation. Theories of emulsification including electric double layer, phase volume, oriented wedge, and surface tension are presented. Methods for determining emulsion type including dilution, dye, conductivity, and fluorescence tests are described. Emulsifying agents and factors influencing emulsion stability are also summarized. Suspensions are defined as biphasic systems with solid particles between 0.5-5 microns dispersed in a liquid. Particle size and sedimentation theories are briefly covered.

1. Disperse Systems
Presented By-
Rohit
R.K.S.D college of pharmacy, Kaithal (Hry)
M.Pharma 1st year
(Pharmaceutics)

2. CONTENTS
1. Introduction and classification.
2. Interfacial phenomenon.
3. Wetting phenomenon.
4. Adsorption.
5. Surface active agents.
6. Micellar solubilzation.
7. Coarse of dispersion systems,
(a) Emulsions (definition, theory, determination of type, emulsifying
agents, stability).
(b) Suspension (definition, types, properties, stability, applications)

3. Introduction
Disperse system:
• Dispersed systems consist of particulate matter, known as the
dispersed phase, distributed throughout a continous or dispersion
medium.
• The dispersed material may range in size from particles of atomic &
molecular dimensions to particles whose size is measured in
millimeters.

4. Classification of dispersed
systems on the basis of particle
size

5. Interfacial phenomenon
• The boundary between two phases is generally described as an
interface.
• When one of the phases is a gas or a vapour, the term surface is
frequently applied.
• In pharmacy, interfacial phenomena play an important role in the
processing of a wide variety of formulations.

6. Wetting phenomenon
• Air may be trapped in the particles of poorly wetted solids which
causes them to float to the surface of the preparation and prevents
them from being readily dispersed throughout the vehicle.
• Wetting of the particles can be encouraged by reducing the interfacial
tension between the solid and the vehicle, so that adsorbed air is
displaced from solid surfaces by liquid.
• The contact angle between a liquid and a solid may be 0° signifying
complete wetting, or may approach 180°, at which wetting is
insignificant.
•The most important action of a wetting agent is to lower the contact
angle between the surface and the wetting liquid.

7. Adsorption
• Adsorption, the binding of molecules or particles to a surface, must be
distinguished from absorption, the filling of pores in a solid.
• The binding to the surface is usually weak and reversible.
• Just about anything including the fluid that dissolves or suspends the
material of interest is bound, but compounds with color and those that
have taste or odour tend to bind strongly.

8. Surface active agents
• A molecule that contains a polar portion and a non polar portion is
called surface active agent/ surfactant.
• A surfactant can interact with both polar and non polar molecules.
• A surfactant increases the solubility of the otherwise insoluble
substances.
• In water, surfactant molecules tend to cluster into a spherical
geometry non polar ends on the inside of the sphere polar ends on the
outside .These clusters are called micelles.
Structure of surfactant

9. Micellar solubilzation
• Micellar solubilization can also increase the solubility of drugs in the
gastrointestinal tract.
• The ability of bile salts to solubilize drugs depends mainly on the
lipophilicity of the drug.

10. Coarse of dispersion
systems
A. Emulsion
B. Suspension

11. 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.

12. Theory of Emulsification
Many theories have been advanced to account for the way or means by
which the emulsion is stabilized by the emulsifier.
1) Electric Double Layer Theory
2) Phase Volume Theory
3) Surface tension Theory
4) Oriented wedge theory

13. ELECTRIC DOUBLE LAYER
THEORY
• When electrode immersed in an electrolytic solution, charge
accumulation will occur.
• Particle size should be greater than 1 nm.
• Charge separation always occur at the interface of the electrodes in
the solution.
• The excess charge on the electrode surface is accumulated by an
accumulation of the excess ions of the opposite charge in the solution.

14. • EDL is a transition region
between two phases consists
of,
1. An inner monomolecular
layer
2. An outer diffuse region
3. A layer intermediate
between inner molecular
layer and the outer diffuse
layer

15. PHASE VOLUME THEORY
It is possible, one sphere can touch 12 others and the volume the
spheres occupy is about 74 per cent of the total volume.
Thus if the spheres or drops of the dispersed phase remain rigid it is
possible to disperse 74 parts of the dispersed phase in the continuous
phase; but if the dispersed phase is increased to more than 74 parts of
the total volume, a reversal of the emulsion will occur.
However, the dispersed phase does not remain rigid in shape but the
drops flatten out where they come in contact with each other, nor are
all the dispersed particles the same, so that it is possible for the
dispersed phase same, so that it is possible for the dispersed phase to
consist of from 1 to 99 per cent of the emulsion.

16. Phase volume diagram.

17. ORIENTED WEDGE THEORY
This theory deals with formation of monomolecular layers of
emulsifying agent curved around a droplet of the internal phase of
the emulsion.
Example:
•In a system containing 2 immiscible liquids, emulsifying agent would be
preferentially soluble in one of the phases and would be embedded in
that phase.
•Hence an emulsifying agent having a greater hydrophilic character will
promote o/w emulsion and vice-versa.
•Sodium oleate is dispersed in water and not oil. It forms a film which is
wetted by water than by oil. This leads the film to curve so that it
encloses globules of oil in water.
•Sodium Oleate, Zinc Oleate

18. Oriented wedge figure.

19. SURFACE TENSION THEORY
• A DROP OF LIQUID FORMS A SPHERICAL SHAPE WHICH GIVES IT THE
SMALLEST SURFACE AREA PER UNIT VOLUME
• WHEN 2 DROPS COME TOGETHER TO FORM A BIGGER DROP- GIVES
LESSER SURFACE AREA. ALSO CALLED SURFACE TENSION AT AIR-LIQUID
INTERFACE
• SURFACE TENSION- FORCE THAT HAS TO BE APPLIED PARALLEL TO THE
SURFACE OF LIQUID TO COUNTER BALANCE EXACTLY THE INTERNAL
INWARD FORCES THAT TEND TO PULL THE MOLECULE TOGETHER.
• WHEN THERE ARE TWO IMMISCIBLE LIQUIDS-IT IS CALLED
INTERFACIAL TENSION.
SURFACE TENSION
Figure.

20. Types of emulsion
• Generally, the two liquids that form an emulsion are an oil and water.
– Two types of emulsion
1.Oil in water emulsion (O/W emulsion): oil is in the dispersed phase
and water in dispersion medium or continuous phase.
2.Water in oil emulsion (W/O emulsion): water is in the dispersed
phase and oil in dispersion medium or continuous phase.

21. Determination of type of
emulsion
• The followings tests are done to distinguish between o/w and w/o
emulsions.
1. Dilution test
2. Dye test
3. Conductivity test
4. Fluorescence test

22. Dilution test
• The emulsion is diluted with water.
• In case the emulsion remains stable after its dilution, it is o/w
emulsion.
• The w/o emulsion breaks on its dilution with water but remains stable
when diluted with oil.

23. Dye test
• The scarlet red dye is mixed with the emulsion.
• Place a drop of the emulsion on a microscopic slide, cover it with a
cover-slip, and examine it under a microscope.
• If the disperse globules appear red and the ‘ground’ colourless, the
emulsion is w/o type.
• The reverse condition occurs in o/w type emulsion i.e., the disperse
globules appear colourless in the red ‘ground’.

24. Conductivity test
• Water is a good conductor of electricity, whereas oil is non-conductor
of electricity.
• The conductivity test can be performed by dipping a pair of electrodes
connected through a low voltage bulb in the emulsion.
• If the bulb glows on passing the electric current, the emulsion is o/w
type, because water is in the continuous phase.
• In case the bulb does not glow, the emulsion is w/o type, because oil is
in the continuous phase.

25. Fluorescence test
• Certain fixed oils possess the physical property of fluorescing in the
presence of ultraviolet radiation.
• On microscopic observation of emulsion under ultraviolet radiation,
the whole field
Fluorescence indicates that oil is present in continuous phase (w/o type
emulsion) and droplets fluorescence indicates that oil is present in
disperse phase (o/w type emulsion).

26. Emulsifying agents
 The emulsifying agents reduce the interfacial tension between two
phases i.e., oily phase and aqueous phase and thus make them
miscible with each other and form a stable emulsion.
 Emulsifying agents are also known as emulgents or emulsifiers.
E.g. Acacia, Glyceryl monosterate, Tragacanth, etc.
Types of emulsifying agents:

27. Stability of emulsion
• An emulsion is said to be stable if it remains as such after its
preparation, i.e., the dispersed globules are uniformly distributed
through out the dispersion medium during its storage.
• Emulsion should be chemically stable and there should not be any
bacterial growth during its shelf life.
• The following three changes usually occurs during the storage of an
emulsion:-
1. Cracking, 2. Creaming, 3. Phase inversion

28. 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.

29. ƒ
Some theoretic considerations are :ƒ
1.Particle size
ƒƒ2.Sedimentation
Theory of Suspension

30. Particle size
Particle size of any suspension is critical and must be reduced within
the range . Too large or too small particles should be avoided.
Larger particles will settle faster at the bottom of the container.
•particles > 5 um impart a gritty texture to the product and also cause
irritation if injected or instilled to the eye
•particles > 25 um may block the needle
•Too fine particles will easily form hard cake at the bottom
of the container

31. SEDIMENTATION
Sedimentation means settling of particle (or) floccules occur under
gravitational force in liquid dosage form.
Velocity of sedimentation expressed by Stoke’s equation
Where,
d = Diameterof particle
r = radius of particle
Vsed.= sedimentation velocity in cm / sec
ρs= density of disperse phase
ρo= density of disperse media
g = acceleration due to gravity
ηo= viscosity of disperse medium in poise

32. Limitation Of Stoke’s Equation
Stoke's equation applies only to:
1. Spherical particles in a very dilute suspension (0.5 to 2 gm per 100
ml)
2. Particles which freely settle without collision
3. Particles with no physical or chemical attraction.

36. If f=fo, then B will be one
If B=1, then the suspension not represent a flocculated system
If B>1, higher the value of B greater the physical stability

37. Brownian movement can be observed , if the size of the particles is
about 2 to 5um, provided densities of the particles, and viscosity of
the medium are favourable.
Particle size and viscosity as the major factors of Brownian movement.

38. Types or classification of
suspensions
1. Flocculated suspension: The suspension are said to be flocculated,
when the individual particles are in contact with each other and form a
network like structure.
2. Non-flocculated suspension: Whereas in case of non-flocculated
suspensions, the individual particle exists as a separate entity.

39. Properties of Suspension
• Uniform particle size: all particles behave alike and produce
consistent behavior for the suspension as a whole.
• No particle-particle interaction: each particle remains discrete with
no aggregation or clumping.
• No sedimentation: drug particles are either stationary or move
randomly thought-out the dispersion medium, so the drug is always
uniformly distributed.
Heterogeneous misture
Scatter light

40. Stability of suspensions
• A stable suspension can be redisperse homogeneously with moderate
shaking and can be easily poured throughout its shelf life.
• The most stable pharmaceutical suspensions are flocculated.
• The sedimented particles of a flocculated suspension can be
redispense easily at any time with only moderate shaking.
• The non-flocculated suspension can be made stable by decreasing the
particle size of the suspended material or by increasing the density and
viscosity of the vehicle.

41. Applications of suspension
• Suspensions can be used as oral dosage form.
• Suspensions can applied topically for the skin.
• Suspensions can applied to mucous membrane
surfaces.
• Suspensions can be given parenterally by injection.
• To improve the stability of drugs.
•To mask the unpleasant taste.
•For delivery of poor soluble drugs.
•In vaccines ,For example diptheria and tetanus vaccines.
•In aerosol: suspension of active agent in mixture of propellants.

42. THANK YOU FOR YOUR
PATIENCE