Surface Active Agent (Surfactant)

A surface active agent (= surfactant) is a substance which lowers the surface tension of the medium in which it is dissolved, and/ or the interfacial tension with other phases, and, accordingly, is positively adsorbed at the liquid/ vapour and/ or at other interfaces. The term surfactant is also applied correctly to sparingly soluble substances, which lower the surface tension of a liquid by spreading spontaneously over its surface.

Surfactants have two distinct regions in their chemical structure, one of which is water-liking or hydrophilic and the other of which is water-hating or hydrophobic. These molecules are referred to as amphiphilic or amphipathic molecules or simply as surfactants or surface active agents. These are compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid.

Pharmaceutical uses of Surfactant (SAA)

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• Surfactant used in emulsions as an emulsifying agent
• Surfactant used in suspensions as a flocculating agent
• Surfactant as a wetting agent
• Surfactant as a bactericidal agent
• Surfactant as a solubilizing agent

Examples of Surface Active Agent

• Potassium laurate
• Sodium lauryl sulfate
• Sorbitan monopalmitate
• Cetrimide
• Benzalkonium chloride

Schematic diagram of a micelle – the lipophilic tails of the surfactant ions remain inside the oil because they interact more strongly with oil than with water. The polar ‘heads’ of the surfactant molecules coating the micelle interact more strongly with water, so they form a hydrophilic outer layer that forms a barrier between micelles. This inhibits the oil droplets, the hydrophobic cores of micelles, from merging into fewer, larger droplets (emulsion breaking) of the micelle.