Spectrophotometric and Calorimetric Studies of the Thermodynamics for the Interaction of Sodium p-Toluenesulfonate with Dodecyltrimethylammonium Bromide Micelles

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The thermodynamic properties for the interaction of sodium p-toluenesulfonate with dodecyltrimethylammonium bromide micelles were studied by spectrophotometric and calorimetric techniques to compare these two methods with each other as a means for the study of such an interaction. Thermodynamic parameters of K = (2.5 ±0.7) x 10^3 M^<-1>, ΔG°= -4.6±0.4 kcal mol^<-1>, ΔH°= -2.1±0.2 kcal mol^<-1> and ΔS°= 8.4 ±0.7 cal deg^<-1> mol^<-1> were obtained by the spectrophotometric method at 25℃. Calorimetric method gave K=(2.0 ± 1.5) x 10^3 M^<-1>, ΔG°= -4.5±1.O kcal mol^<-1>, ΔH°= -1.40±0.09 kcal mol^<-1> and ΔS°= 10±3 kcal mol^<-1> at the same temperature. The results suggest that the spectrophotometric method is recommended for the determination of equilibrium constant and standard free energy change and calorimetric method for the measurement of standard enthalpy change. Entropy change had better be evaluated by the combination of two methods. Though the calorimetric method produced larger errors in the present study because of the small heat of the interaction, it would be useful for the study of the interactions of the systems which evolve the appreciable heat and to which the spectrophotometric method is not applicable.
琉球大学理学部の論文