Experiments on electrical conductivity in aqueous solutions of cationic gemini surfcatants as a function of concentration and temperature were carried out, where two species of alkdimethylammonium bromide [C~mH~2m+N(CH~3)~2·Br,m=8,10, 12,]were linked at the polar head groups via a hydrocarbon spacer [(CH~2)~s , s=2,3,4,6,]. Critical micelle concentration (cmc) was obtained from the break point in the curve of conductivity k vs concentration c. The results indicate that the trend of micelle formation of the gemini surfactants is significantly stronger that the corresponding "monomer", i. e. alkyltrimethylammonium bromide. The change of Gibbs free energy, enthalpy and entropy in the process of micellization were evaluated based on a mass action model. The results show that micellization of the gemini surfactants is an entropy -driven process, which is similar to concentional surfactants. All plots of enthalpy - entropy compenstion exhibit excellent lineatity. The intercept of compensation of the gemini surfactants decreases with the decrease of s from 6 to 2. The implies that the gemini surfactants with short spacer tend to form stable micelles.

Key words: SURFACTANTS, ENTHALPY, ENTROPY