ABSTRACT
The first reports on gemini surfactants concerned bisquaternary ammonium halide surfactants. Their biological activity in aqueous solution was studied [13,16,17], and micellar solutions of these surfactants were used to catalyze chemical reactions [18]. Most studies, however, reported on the surface tension of the aqueous solutions of gemini surfactants for CMC determinations and an assessment of their capacity in reducing the surface tension of water [3,5-8]. These studies did not raise much interest among surfactant scientists in spite of the much lower CMC and stronger biological activity found for gemini surfactants compared with the corresponding monomeric conventional surfactants. It was only in the early 1990s, following the synthesis of gemini surfactants in a great variety of chemical structures, that more systematic studies revealed that such surfactants possess properties that make them superior to conventional surfactants [14]. Thus, their values of C20, the surfactant concentration where the surface tension is decreased by 20 mN/m, are much lower for equal or lower values of 'YcMc (surface tension at the CMC) [14]. The idea underlying the study of gemini surfactants is that linking surfactants two by two may provide a new way to control the shape of their assemblies and thus some of their properties [ 19].
