Surfactants

Abstract

The inclusion of a volume dealing with the properties of solutions in a comprehensive treatise on water is understandable in view of the known effects of water “structure” on intermolecular interactions in aqueous solutions. It is worthy to mention at this point that Frank⁽⁴⁷⁶⁾ recently suggested that the study of aqueous solutions in general (and one might include nonaqueous solutions) will likely increase our presently incomplete understanding of water itself. Surface-active molecules, which characteristically contain a polar and a relatively large nonpolar portion, are known as surfactants, and their solutions in particular are attractive for study since they include a wide variety of solute molecules which may be conveniently studied by a wide variety of physical techniques. The ability of the polar portion of the surfactant molecule to increase the solubility of the nonpolar side chain makes it possible to determine experimentally the effects of normally sparingly soluble groups on the properties of water itself, subject to a determination of the contribution of the polar portion (head group effect). An estimation of the importance of the head group effect can be made by comparison of the solution properties of nonpolar solutes and surfactants. Finally, a study of several fairly well-defined types of molecular association with surfactants may allow a distinction to be made between the contributions of the solute and the solvent to the observed bulk properties of the solutions.