CALORIMETRIC CHARACTERIZATION OF HEXADECANESULFONIC ACID AQUEOUS SYSTEMS

The hexadecanesulfonic acid aqueous system was investigated by determination of the concentration-temperature regions where ionic solution, solid, gel and micellar phases exist. The temperature dependency of the c.m.c., solubility and heat of dilution provided information on the characteristics of these phases. The calorimetry was performed so that concentrated systems were diluted to ionic solutions of low concentration. These results agreed with the phase diagram. The interpretation was based on the thermodynamic relationships which include the change in heat capacity. The solid phase has a lower heat capacity than dissolved ions, while the gel and micellar phases are characterized by a higher heat capacity. The standard enthalpy at a reference temperature of 25°C for solid, gel and micelle dissolution/dissociation was found to be positive, indicating an endothermic processes. © 1990.