Abstract: Mixed micellization of quaternary ammonium dimeric surfactants, C12sC12•2Br(s=2,3,4,6), and a nonionic surfactant C12E10 or C12E23 in aqueous solution have been investigated using conductivity measurement. The results show that C12sC12•2Br and C12E10 or C12E23 form mixed micelles. The values of the total critical micelle concentration lie always among and , which are the critical micelle concentrations for individual surfactant 1 and surfactant 2, respectively. Addition of a few nonionic surfactant, for example α2=0.1, the molar fraction of C12E10 or C12E23 in the mixed micelle exceeds 0.35. With further increasing the concentration of the nonionic surfactant in solution, the main component in the mixed micelles becomes gradually C12E10 or C12E23.

Key words: Quaternary ammonium dimeric surfactants, C₁₂E₁₀, C₁₂E₂₃, Mixed micelle