THERMODYNAMICS OF N,N,N-OCTYLPENDYLDIMETHYLAMMONIUM CHLORIDE IN WATER-UREA MIXTURES

摘要

Specific conductivities, densities, heat capacities, and enthalpies of dilution at 25 degrees C were measured for N,N,N-octylpentyldimethylammonium chloride (OPAC) in water-urea mixtures at various urea concentrations m(u) as functions of the surfactant concentration m,. From conductivity data, the cmc and the degree of the counterion dissociation beta of the OPAC micelles were calculated. The cmc increases linearly with increasing m(u) while beta vs. m(u) is a smooth concave curve. From the experimental thermodynamic data, the apparent (Y-phi) and partial (Y-2) molar properties (volumes, heat capacities, and relative enthalpies) are derived as functions of m(u) and m(2). The effect of urea on the dependences of the different properties on m(s) are discussed. From data in the premicellar region the standard partial molar volumes V-2(0) and heat capacities C-p2(0) were evaluated. It was observed that V-2(0) increases linearly with m(u) while C-p2(0) decreases. The properties of OPAC in the dispersed and micellized forms at the cmc were obtained and, therefore, the thermodynamic functions of micellization were calculated on the basis of the pseudo-phase transition model. [References: 30]