Definition Application Difference between molecular and Colloidal dispersion Characteristics of dispersed phase Classification of colloidal dispersion Purification of colloidal dispersion

1. Colloids
Prepared by ,
Mr. Snehal Patel
Assistant Professor,
Sumandeep Vidyapeeth,
Vadodara, Gujarat, India.

2. Content
• Definition
• Application
• Difference between molecular and Colloidal dispersion
• Characteristics of dispersed phase
• Classification of colloidal dispersion

3. Definition
• A colloidal system is dispersion wherein dispersed particles (internal
phase) are distributed uniformly in a dispersion medium (external phase).
• The word colloid comes from a Greek word 'kolla', which means glue thus
colloidal particles are glue like substances.
• Colloidal system are defined as those polyphasic system.
• Dimension of the dispersed phase measures between 10-100 A to a few
micrometers.
• Colloids can be made settle by the process of centrifugation.

6. Examples of colloids
• Milk
• Foam
• Aerosol
• Blood
• Fog
• Butter
• Ice cream
• etc

7. Application of colloids
1. Therapy: Some colloidal dispersion show better therapeutic action
and are used in treatment.
Silver colloid – germicidal
Copper colloid – anticancer
Mercury colloid – antisyphilis
2. Absorption and toxicity:
• Colloidal sulfer shows better and faster absorption compared to a
coarse dispersion of sulfer.
• Complete absorption of sulfer from the colloidal dispersion results in
high concentration in the blood, which often leads to toxicity.

8. Application of colloids
3. Solubility: Solubility of drug is improved by using colloidal systems
containing surface active agents.
4. Stability: Dispersion of surface active agent (associated colloids) are
used to improve the stability of drugs in liquid dosage forms.
5. Targetting of the drug to the specific organs:
• Colloids are used in targeting the drug to specific body organs.
• For example, drug entrapped liposomes are being preferentially take
up by the liver and spleen. Other colloidal drug delivery systems
include carrier systems such as liposomes, niosomes, nanoparticles
and micro-emulsion.

9. Distinguish between molecular and colloidal
dispersion
Property Molecular Dispersion Colloidal Dispersion
Size of particle Less than 1 nm 0.5mm to 1 nm
Visibility
Not visible even with electron
microscope
Visible with ultra microscope
and electron microscope
Scattering of light Does not scatter Scatter and shows tyndall effect
Transport across semipermeable
membrane
Permeable Impermeable
Settling
Does not settle on
ultracentrifugation
Settle on ultracentrifugation
Diffusion rate Rapid slow

10. Characteristics of Dispersed Phase
1. Particle size
• Particle size influences the colour of the dispersion.
• For eg: colloidal gold has red colour, while intermediate size is violet
colour. The coarse dispersion of gold appears blue.
2. Particle shape
• The shape of particle in dispersion depends on the method of
preparation and affinity of the particles to the dispersion medium.
• Shape also influences the colour of the dispersion. It is believed that
spherical particle of gold is indicated by red colour, while disc like
particle of gold gives blue colour.

11. Particle shape

12. 3. Surface area
• As the size of the colloidal particles is of the order of a few
micrometers, these particles possess enormous surface area, when
compared to the coarse particles.
• Their large surface area make them effective catalysts.
• The larger surface area enhances the solubility of the drug particle.
4. Surface Charge
• Colloidal particles possess charge on their surfaces.
Negative Positive
Acacia Gelatin
Sulfur Bismuth
Tragacanth Aluminium

13. • The charge on these particles and its environment in adispersion medium is
shown in the figure.
• The interior of these particles is electronically neutral, but the surface
becomes charged.
• The reason for the origin of the charge on the surface of particle is
1. Functional group –COOH present on the surface may get ionised.
2. Ions present in the medium may gets adsorbed onto the surface of the
particles. Even in pure water either OH- or H+ ions may gets adsorbed to
the surface of the particles.

14. • Surface charge provides valuable information regarding the stability
of the colloids. Particles move continuously in random manner with
collision with each other.
• The like charge of the particles creates repulsion forces. During these
collosions, particles remain as individual entities and distributed
uniformly. Thus stability of colloids is attributed to surface charge.

15. Classification of colloidal dispersion
1. Lyophilic colloids
2. Lyophobic colloids
3. Associated colloids

17. Association colloids
• Amphiphiles are the molecules or ions which have certain affinity for
both polar and non polar solvents.

18. • In water, at low concentrations, surface active agent exist as individual
monomer.
• As the concentration increases, the monomer aggregate themselves over a
narrow range of concentration. These aggregates are called as miscelles.
• Each miscelle may contain around 50 monomers, and size may be around 50 Å.

19. Critical micelle concentration (CMC)
• CMC is difined as the concentration range of of a surfactant at which
miscelle starts forming.

20. Krafft Point, Kt
• Krafft point is defined as the temperature at which the solubility of
the surfactant is equal to the cmc.

21. Purification of Colloidal Dispersion
• Dialysis
• Electrodialysis
• Ultrafiltration

22. Dialysis
• It’s principle is that colloidal particles can not
pass through a cellophane membrane while
the ions of the electrolyte can pass through it.
• The impurities slowly diffused out of the bag
leaving behind pure colloidal solution.
• The distilled water is changed frequently to
avoid accumulation of the crystalloids
otherwise they may start diffusing back into
the bag.
• Dialysis can be used for removing HCl from
the ferric hydroxide sol

23. Electrodialysis
• The process of dialysis is very slow.
• The process is speeded up by application
of electrical potential.
• This is called electro dialysis.
Application
• Artificial kidney machine make use of
electro dialysis.

24. Ultrafiltration