Adsorption at liquid interface: Positive adsorption, Negative adsorption. SURFACE ACTIVE AGENT, Classification of surfactant Ionic surfactants: Anionic surfactant, Cationic surfactant, Ampholytic / Amphoteric surfactant. Non Ionic Surfactants:

1. IIIrd Semesester B. pharmacy
Physical Pharmaceutics-I
Unit-III
Surface and Interfacial tension [Part-4]
(Adsorption at liquid interface, Surface active agents )
Miss. Pooja D. Bhandare
(Assistant professor)
Kandhar college of pharmacy

2. Adsorption at liquid interface:
• Adsorption is defined as the deposition of some molecule or ions
(molecular species) onto the surface of the liquid.
• Certain solute molecule and ions when added in a liquid are partitioned
in favour of surface or the interface.
This is termed as positive adsorption.
• Some other solute molecules or ions partitioned in favour of bulk of the
liquid.
This term as negative adsorption

3. • Positive adsorption
 Molecule deposit on the surface
of liquid.
Surface free energy and surface
tension decreased.
Molecule settle down on surface.
• Negative adsorption
Molecule does not deposit on
surface it mix with the liquid.
Surface free energy and surface
tension increased.
Molecule mixed with liquid.

4. SURFACE ACTIVE AGENT
• Molecule or ions that are adsorbed at the interface are termed as
surface active agent or surfactant.
• Surface are amphiphiles . They contain a polar head or nonpolar tail.
• Surfactant may be hydrophilic if it is predominantly polar in nature
and lipophilic if it predominantly non polar

5. • When surfactant is added to water.
Hydrophilic head will be oriented towards water.
Lipophilic are will be oriented away from water

6. • When a surfactant is added on these system
Hydrophilic head will be oriented towards aqueous phase.
Lipophilic tail oriented towards oil phase.

7. Classification of surfactant
Surfactant
Ionic Non ionic
Cationic Ampholytic
Anionic

8. A. Ionic surfactants
1. Anionic surfactant.
• It ionises in aqueous solution to yield a large anion and a small cation.
• The long chain anion of these surfactants import surfaceactivity.
• Cation is inactive.
• Examples: Potassium stearate soap, Sodium cetyl sulphonate.

9. 2. Cationic surfactant
• It ionises in aqueous solution to yield positively charged cations.
• Quaternary ammonium compound such as cetrimide, benzalkonium
chloride are examples
• Mainly used antiseptics, disinfecting agents.
• Also used as secondary emulsifying agents for external application.

10. 3. Ampholytic / Amphoteric surfactant
• Contains carboxylate / phosphate group / anion ammonium/
Quaternary ammonium groups as cation.
• Ionic characteristics depends on the pH of system.
• Below the certain pH, these are cationic while above a defined pH,
these are anionic.
• Examples : N- dodecyl alanins, lecithin.

11. B. Non Ionic Surfactants
• They do not ionise in aqueous solutions.
• Largest group of surface active agents that is useful pharmaceutically.
• Example: Glycerol and Glycol esters such as glycerol monostearate
and propylene glycol monostearate.
• Span, tweens (polysorbates)