Aggregation, adsorption, and clouding behaviors of Triton X-100 in formamide.

The critical micelle concentration (cmc) of TX-100 in formamide (FA) was determined from surface tension measurements as functions of temperature and NaCl concentration. At 25 degrees C, cmc was also determined by the fluorescence method. For the sake of comparison, micellization parameters of TX-100 were also determined in water. cmc, aggregation number, and standard free energy of micellization in FA are about 400 times higher, 10 times lower, and 2 times higher than in water, respectively. On increasing the temperature, cmc in FA shows a slight increase, whereas in water it decreases. The logarithm of relative cmc decreases linearly with added NaCl concentration in both FA and water, and the rate of this decrease is surprisingly equal in the two solvents. Micellization of TX-100 is exothermic in FA, but endothermic in water. The cloud point (CP) of TX-100 was determined in FA+water medium and that in pure FA was estimated to be approximately 233 degrees C when [TX-100]=0.15 mol kg(-1). Surface excess values of TX-100 were calculated from Gibbs and Langmuir adsorption isotherms. Values of standard free energy of adsorption calculated from the Rosen-Aronson equation and from the Langmuir adsorption isotherm are comparable. The ratio of the surface tension of the solvent to that at the cmc has been demonstrated as a novel scale for measuring solvophobicity.