Introduction

Gemini (also called dimeric) surfactants represent a new class of surfactants made up of two identical or different amphiphilic moieties having the structure of conventional (monomeric) surfactants connected by a spacer group [1]. The spacer may be hydrophobic (aliphatic or aromatic) or hydrophilic (polyether), short (two methylene groups) or long (up to 20 and more methylene groups), rigid (stilbene) or flexible (polymethylene chain). Figure la gives a schematic representation of a gemini surfactant. At the outset, it must be emphasized that the spacer group must connect the two amphiphilic moieties at the level of, or in close vicinity to, the head groups. If the connection takes place in the middle or toward the end of the alkyl chains of the amphiphilic moieties as in Fig. 1b, the surfactant is then a bolaform surfactant endowed with properties that are inferior to those of conventional surfactants.