EFFECT OF LARGE CHANGES IN TEMPERATURE AND PRESSURE ON THE THERMODYNAMIC PROPERTIES OF MICELLIZATION AND ON THE DISTRIBUTION CONSTANT OF A POLAR SOLUTE IN MICELLAR SOLUTIONS

Density measurements of pentanol (PentOH)-dodecyltrimethylammonium bro mide (DTAB)-water mixtures as functions of both alcohol and surfactant (ms) concentrations were carried out at 0.1 MPa from 45 to 75 degrees C and at 19 MPa from 25 to 130 degrees C. The standard (infinite dilu tion) partial molar volumes and expansibilities of DTAB in water and t he corresponding properties in the micellar phase were calculated from the experimental data. As far as PentOH in DTAB micellar solutions is concerned, with the exception of the standard partial molar volume (V OR) data at 130 degrees C and 19 MPa, all the VOR VS ms trends are mon otonic curves with ms The data of VOR as a function of ms were treated by means of an equation previously used for data obtained at ambient conditions. So it was possible to evaluate simultaneously the distribu tion constant (K) of PentOH between the aqueous and micellar phases an d the standard partial molar volume of alcohol in the aqueous (V-R,f(0 )) and the micellar (V-R,m(0)) phases. The standard free energy of tra nsfer (Delta G(t)(0)) of PentOH from the aqueous to the micellar phase s was calculated from K values. By using experimental literature data for the present system at 25 degrees C, Delta G(t)0 values as function s of temperature and pressure were calculated. The very good agreement between the simulated and experimental values indicates that the mode l used also holds at higher temperatures. Equations correlating the st andard free energy, enthalpy, and entropy of transfer to temperatures up to 130 degrees C and pressures up to 19 MPa were proposed.