Physical Pharmaceutics - Colloids - Part 1

1. Stability of Colloids
Dr. A. SUMATHI
Professor & Head
Department of Pharmaceutics

2. Stability of Colloids
 The presence & magnitude or absence of a charge on a colloidal
particle is an important factor in the stability of colloidal system
 Lyophilic sols
 These are stabilized by the presence of charge on the colloidal
particles & surrounding of each particle with a solvent sheath
that prevents mutual adherence
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Dr. A. SUMATHI COLLOIDS

3. Stability of Colloids
 Lyophobic sols
 These are thermodynamically unstable
 The like charges produce a repulsion that prevents
coagulation of the particles
 Addition of a small amount of electrolyte that stabilizes by
imparting a charge on the particles
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Dr. A. SUMATHI COLLOIDS

4. Stability of Colloids
DLVO Theory
 Derjaguin Landau Vervey Overbeek Theory
 The forces on colloidal particles in a dispersion are due to
electrostatic repulsion & London type Vander Waals forces of
attraction
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Dr. A. SUMATHI COLLOIDS

5. DLVO (Derjaguin Landau Vervey Overbeek) Theory
 These forces result in potential energies of Repulsion (VR) &
Attraction (VA) between the particles
 There is a attraction near the origin & a high potential barrier of
repulsion at moderate distances
 A shallow secondary attraction is sometimes observed at longer
distances of separation
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Dr. A. SUMATHI COLLOIDS

6. DLVO (Derjaguin Landau Vervey Overbeek) Theory
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Dr. A. SUMATHI COLLOIDS

7. Stability of Colloids
 Addition of electrolyte can bring about coagulation of colloidal
particles
 The mixing of oppositively charged colloids will result in mutual
agglomeration
 If salt is sufficiently added to Lyophilic colloids, agglomeration &
sedimentation of the particles will result. This phenomenon is
called Salting out
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Dr. A. SUMATHI COLLOIDS

8. Sensitisation & Protective Colloidal Action
 The addition of small amount of Hydrophilic or Hydrophobic
colloid to a Hydrophobic colloid of opposite charge will sensitize or
coagulate the particles
 This is due to reduction of zeta potential below the critical value
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Dr. A. SUMATHI COLLOIDS

9. Sensitisation & Protective Colloidal Action
 The addition of large amount of Hydrophilic substances stabilizes
the system
 Hydrophiles being adsorbed on the Hydrophobic particles
 This phenomenon is known as Protection and the added
Hydrophilic sols are called as Protective Colloids
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Dr. A. SUMATHI COLLOIDS

10. GOLD NUMBER
 It is the minimum weight in milligrams of the protective colloid
required to prevent a colour change from red to violet in 10 ml of a
Gold sol on the addition of 1 ml of a 10 % solution of Sodium
chloride
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Dr. A. SUMATHI COLLOIDS

11. Thank You
 Dr. A. SUMATHI