Dispersed Systems - Classification & their general characteristics; Colloids - Classification & comparative account of their general properties

1. UNIT-I
Colloidal dispersions
Dr. A. SUMATHI
Professor & Head
Department of Pharmaceutics
PHYSICAL PHARMACEUTICS-II
FOURTH SEMESTER B.PHARM

2. COLLOIDAL DISPERSIONS
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▹ Classification of dispersed systems & their general
characteristics
▹ Size & shapes of colloidal particles
▹ Classification of colloids & comparative account of their general
properties
▹ Optical, kinetic & electrical properties
▹ Effect of electrolytes, coacervation, peptization & protective
action
Dr. A. SUMATHI

3. DISPERSED SYSTEMS
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▹ Dispersed systems consist of particulate matter, known as the
dispersed phase, distributed throughout a continuous or
dispersion medium
Dr. A. SUMATHI

4. CLASSIFICATION OF
DISPERSED SYSTEMS

5. CLASSIFICATION OF DISPERSED SYSTEMS
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Basis of mean particle diameter
▹ Molecular dispersions – Homogeneous system – form True solutions
▹ Colloidal dispersions
▹ Coarse dispersions
Dr. A. SUMATHI
Heterogeneous system

6. Classification of dispersed systems on the basis of particle size
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Parameters Molecular dispersions Colloidal dispersions Coarse dispersions
Particle Size
Range
Less than 1.0 nm 0.5 µm to 1.0 nm Greater than 0.5 µm
Characteristics
of System
 Particles invisible in electron
microscope
 Pass through ultrafilter &
semipermeable membrane
 Undergo rapid diffusion
 Particles are not resolved by
ordinary microscope; May be
detected under ultra
microscope; Visible in electron
microscope
 Pass through filter paper; but
do not pass semipermeable
membrane
 Diffuse very slowly
 Particles visible under
microscope
 Do not pass through normal
filter paper or dialyze through
semipermeable membrane
 Particles do not diffuse
Examples
Oxygen molecules
Ordinary ions
Glucose
Colloidal Silver Sols
Natural & Synthetic Polymers
Grains of sand
Pharmaceutical emulsions &
suspensions
Red blood cells
Dr. A. SUMATHI

7. Classification of colloids &
comparative account of their general
properties

8. Colloids - Comparative account of their general properties
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Lyophilic Association (Amphiphilic) Lyophobic
Dispersed phase consists of large organic
molecules lying within colloidal size range
Dispersed phase consists of
aggregates (micelles) of small
organic molecules or ions whose
size individually is below the
colloidal range
Dispersed phase consists of
inorganic particles, such as Gold or
Silver
Molecules of the dispersed phase are
solvated, i.e. they are associated with the
molecules comprising the dispersion
medium
Hydrophilic or lipophilic portion of
the molecule is solvated,
depending on whether the
dispersion medium is aqueous or
nonaqueous
Little interaction (solvation)
between particles and dispersion
medium
Molecules disperse spontaneously to
form colloidal solution
Colloidal aggregates are formed
spontaneously when concentration
of amphiphile exceeds the critical
micelle concentration (CMC)
Material does not disperse
spontaneously & special
procedures must be adopted to
produce colloidal dispersion
Dr. A. SUMATHI

9. Colloids - Comparative account of their general properties
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Lyophilic Association (Amphiphilic) Lyophobic
 Viscosity of the dispersion medium is
greatly increased by the presence of
the dispersed phase
 At sufficiently high concentrations,
the sol may become a gel
 Viscosity & gel formation are related
to solvation effects & to the shape of
the molecules, which are usually
highly asymmetric
Viscosity of the system increases as
the concentration of the amphiphile
increases, as micelles increase in
number & become asymmetric
Viscosity of the dispersion medium
is not greatly increased by the
presence of the lyophobic colloidal
particles, which tend to be
unsolvated & symmetric
Dr. A. SUMATHI

10. Colloids - Comparative account of their general properties
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Lyophilic Association (Amphiphilic) Lyophobic
 Dispersions are stable in the
presence of electrolytes
They salted out by high
concentrations of very soluble
electrolytes
 Effect is due to solvation of
lyophilic molecules
In aqueous solution, the CMC is
reduced by the addition of electrolytes
 Salting out occur at higher salt
concentration
Lyophobic dispersions are unstable
in the presence of even small
concentrations of electrolytes
 Effect is due to neutralization of
the charge on the particles
 Lyophilic colloids exert a protective
effect
Dr. A. SUMATHI

11. Classification of Association
(Amphiphilic) Colloids

12. Classification of Association (Amphiphilic) Colloids
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TYPE COMPOUND AMPHIPHILE
Anionic Sodium lauryl sulphate CH3(CH2)11OSO3
Cationic Cetyl trimethylammonium bromide CH3(CH2)15N+(CH3)3
Nonionic Polyoxyethylene lauryl ether CH3(CH2)10CH20(CH2OCH2)23H
Ampholytic Dimethyldodecyl ammoniopropane sulfonate CH3(CH2)11N+(CH3)2(CH2)3OSO2
Dr. A. SUMATHI

13. Size & shapes of colloidal particles

14. 14
Purification or
Separation of
Colloids
 Dialysis
 Ultrafiltration
 Electrodialysis
It is important since it
is slightly bigger than
coarse particles &
slightly smaller than
solutions
Dr. A. SUMATHI

15. THANKS!
Any questions?
You can find me at drsumathi2k17@gmail.com
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Dr. A. SUMATHI
Professor & Head
Department of Pharmaceutics