Heat capacities, volumes and solubilities of pentanol in aqueous surfactant solution

Apparent molar heat capacities and vols. of pentanol 0.05 m in dodecyltrimethylammonium chloride (DTAC), dodecyldimethylammonium chloride (DDAC) and dodecylamine hydrochloride (DAC) micellar solns. were measured at 25°. The distribution const. between the aq. and the micellar phase and heat capacity and vol. of pentanol in both phases were derived. The presence of Me groups on the surfactant head group does not appreciably influence the apparent molar volume and heat capacity of pentanol in micellar phase and the free energy of transfer of pentanol from the aq. to the micellar phase. The apparent molar heat capacities of pentanol in micellar solns. as a function of surfactant concn. show evidence of two max. for DAC and of one max. for DTAC whereas no max. were detected for DDAC. These max. can be ascribed to the presence of structural post-micellar transitions. By comparing data for DTAC with those for the corresponding bromide, the role of the counterion nature in the thermodn. of solubilization of pentanol in micellar solns. is derived.