6533b853fe1ef96bd12ac168

RESEARCH PRODUCT

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

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Density measurements of pentanol (PentOH)−dodecyltrimethylammonium bromide (DTAB)−water mixtures as functions of both alcohol and surfactant (mS) concentrations were carried out at 0.1 MPa from 45 to 75 °C and at 19 MPa from 25 to 130 °C. The standard (infinite dilution) partial molar volumes and expansibilities of DTAB in water and the 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°R) data at 130 °C and 19 MPa, all the V°R vs mS trends are monotonic curves with mS. The data of V°R 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 distribution constant (K) of PentOH between the aqueous and micellar phases and the standard partial molar volume of alcohol in the aqueous (V°R,f) and the micellar (V°R,m) phases. The standard free energy of...