Abstract: With increasing the number of oxyethylene groups in the spacer of [C12H25N＋(CH3)2]2C2H4(OC2H4)n•2Br－(C12-2-En-C12•2Br, n=2,3), the homogeneous regions in the phase diagrams of aqueous mixture of C12-2-En-C12•2Br with C12H25SO4Na (SDS) expand obviously in comparison with that of [C12H25N＋(CH3)2CH2]2•2Br－/SDS mixed system. There exists a synergism between C12-2-En-C12•2Br and SDS during the mixed micellization. The minimum critical micelle concentration (cmcT,min) in the homogeneous region is 0.0339 mmol•L－1 and the corresponding molar fraction (x2*) of SDS in the bulk solution is 0.447 estimated by Rosen theory. At x2=0.5, the corresponding molar fraction (x2M) in the mixed micelle and the total aggregation number (NT) are 0.43 and 36 respectively.

Key words: C₁₂-2-E_n-C₁₂•, 2Br, SDS, Phase behavior, Mixed micellization, Synergism