Abstract:
The micellization of methyldodecylbenzyltrimethylammonium chloride (MDBTACL) in water was studied by means of surface tensiometry. The critical micellar concentration (CMC) was determined at 25°, 32° and 40°C and thermodynamic properties such as the free energy of micellization (∆G°mic), enthalpy (∆H°mic), and entropy (∆S°mic) of micellization were measured The CMC at 25°C was 1.12 x 10-2 M and the corresponding values of the thermodynamic parameters were: ∆G°mic = -2.66 kcal/mol; ∆H°mic = -0.82 kcal/mol and ∆S°mic = +6.17 e.u. Micelles of the surfactant MDBTACL were good catalysts for the alkaline hydrolysis of p-nitrophenyl diphenyl phosphate (NPDPP) with a maximum catalytic factor of approximately 60, comparable to that of CTAB. Typical activation parameters measured for 0.012 M surfactant and 0.005 M NaOH were: Ea = 8.5 kcal/mol; ∆H°≠ = 7.8 kcal/mol; ∆G°≠ = 19.6 kcal/mol and ∆S°≠ = -39. 3 e.u. The kinetic results were also analyzed in terms of the pseudo-phase ion-exchange models (PPIE) and showed that the model is applicable and gave reasonable fits.