ABSTRACT
A surfactant is popularly visualized as a surface-active agent that alters the surface properties of a solution, resulting in its multifarious effects and bene“ts. Surfactants are added to a solution to change its surface tension by minimizing the effective free surface energy of the interfaces. The adsorption of a surfactant molecule is driven by lowering of the interfacial tension in the phase boundary. The degree of surfactant adsorption at the interface depends on surfactant structure and the nature of the two phases that meet the interface.1 A surfactant molecule is typically a long hydrocarbon chain or an aromatic ring with a functional group acting as its head. Typically, the tail is derived from an unsaturated high molecular weight fatty acid or its derivatives. The presence of an electrophilic or nucleophilic group is responsible for its hydrophilic nature; consequently, the tail acts as a hydrophobic end of the molecule. The hydrocarbon chain interacts weakly with the water molecules in an aqueous environment, whereas the polar or ionic head group interacts strongly with water molecules via dipole or ion-dipole interactions. It is this strong interaction with the water molecules that renders the surfactant soluble in water. However, the cooperative action of dispersion and hydrogen bonding between the water molecules tends to squeeze the hydrocarbon chain out of the water, and hence these chains are referred to as hydrophobic. For a compound to be a surfactant, it should possess three characteristics: the molecular structure should be composed of polar and nonpolar groups, it should exhibit surface activity, and it should form selfassembled aggregates (micelles, vesicles, liquid crystalline, etc.) in liquids.
