ABSTRACT
Surface-active agents (surfactants) are substances which, at low concentrations, adsorb onto the surfaces or interfaces of a system and alter the surface or interfacial free energy and the surface or interfacial tension. This chapter focuses on the wide range of uses for surfactants in pharmaceutical products and systems. Surface tension reduction by surfactants at the airaqueous interface occurs due to adsorption of surfactants at the interface, with the hydrophilic end of the surfactant oriented toward the liquid. Adsorption of surfactant from an aqueous solution onto a solid surface may involve specific chemical interaction between the surfactant (adsorbate) and the surface (adsorbent). The effect of surfactants on the wetting process is a result of their adsorption at various interfaces with a resulting alteration of interfacial tensions. Surfactant molecules may be classified based on the nature of the hydrophilic group within the molecule, anionic surfactants, cationic surfactants, ampholytic surfactants, and nonionic surfactants.
