Abstract: Sodiumbenzenesulfonate (SNzS) and sodiumnaphthalenesulfonate (SNphS) added in the solution strongly associated with quaternary ammonium gemini surfactants (C12-s-C12·2Br), which increased the hydrophobicity of C12-s-C12·2Br molecule and obviously enhanced their adsorption at the air/water interface and aggregation in the solution. This resulted in great increase in the efficiency and the effectiveness in surface tension reduction, and the formation of small aggregates in the solution at very low concentration of surfactant. Thus, the cmc obtained by surface tension method was only of apparent significance and it reflected the critical concentration when the surfactant reaching saturated adsorption at the air/water interface. Compared with SNzS, SNphS promoted more effectively both adsorption and aggregation of C12-s-C12·2Br due to its higher hydrophobicity.

Key words: C12-s-C12·2Br, Organic counter-ion, Surface activity