Heat capacities and the two-point scaling analysis of short-chain surfactant solutions

The apparent molar heat capacities of two short-chain surfactants (C6TAB and C8TAB) aqueous solutions were determined at four temperatures. For the hexyltrimethylammonium bromide no structural transition was observed. For the octyltrimethylammonium bromide a maximum of the apparent molar heat capacity was observed, which corresponds to the monomer to micelle transition. The two-point scaling theory, that describes the thermodynamics of the system, which can appear in two phases in the vicinity of critical point, was applied to analyse this system. The critical molalities and critical indices were obtained. Comparison of these values with those previously reported for other similar systems allowed to relate them with structure changes in the solution.