VOLUMES AND HEAT-CAPACITIES OF SODIUM PERFLUOROALKANOATES IN WATER

The apparent molar volumes and heat capacities of sodium perfluoroalka noates, NaCF3(CF2)(x)COO, for x equal to 0, 1, 2, 4, and 6, were measu red in water at 25 degrees C, and also at 5 and 55 degrees C in the ca se of NaCF3(CF2)(6)COO, from densities and heat capacities per unit vo lume. The CF2 contribution to the standard partial molar volumes and h eat capacities are (23.57 +/- 0.05) cm(3) . mol(-1) and (124 +/- 1) J . K-1. mol(-1), respectively. The data for NaCF3(CF2)(4)COO and NaCF3( CF2)(6)COO were analyzed with a mass-action model to obtain the thermo dynamic properties of micellization of the surfactants. The volumes an d heat capacities of micellization at 25 degrees C are respectively (8 .8 and 11.2) cm(3) . mol(-1) and (-443 and -587) J . K-1. mol(-1). At 5 degrees C, NaCF3(CF2)(6)COO is too close to the Krafft temperature t o obtain data for the surfactant in the micellized form. At 55 degrees C, the volume and heat capacity of micellization are significantly sm aller in magnitude than those at 25 degrees C.