The results of thermodn. study at 313 K in aq. solns. of some amphiphilic betaine chloride ester derivs. (Cn-BEC, n = 10, 12, 14) (showing biol. activity) are reported for the 1st time. Diln. enthalpies were measured by a flow type microcalorimeter, the d. (at 298 and 313 K) was measured by using a vibrating tube densimeter, and the osmotic coeffs., by a vapor pressure osmometer. Apparent and partial molar quantities were obtained from the exptl. data and expressed as a function of molalities, assuming the infinite diln. as std. state. The enthalpies and molar vols. of micellization were evaluated graphically on the basis of the pseudo-phase sepn. model. The heat capacities of micellization were also obtained by using the calcd. enthalpies of micellization at 313 K and previously reported values for 298 K. The general thermodn. trend as a function of chain length is comparable with that of other homologous series of cationic surfactants, in spite of the presence of the carboxyl group. For this class of surfactants, too, the additivity rule seems to hold. For all the properties studied, the CH2 group contributions are comparable with those reported in the literature for other classes of cationic surfactants, despite the presence of the carboxylic group between the charged head and the hydrophobic tail. In micellar solns., the COO group contribution to vol. is 22.4 cm3 mol-1 compared to 16.3 cm3 mol-1 for each CH2. The comparison of the trends of thermodn. quantities of C10-BEC with those of dodecyltrimethylammonium chloride (DTAC) supports the hypothesis that 2 methylene groups of DTAC and the -CH2-COO- group of the betaine ester derivs. are not incorporated into the micelle core.
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