PHYSICAL CHEMICAL STUDIES OF THE SURFACTANT DILAURYLDIMETHYLAMMONIUM BROMIDE (DLDMAB): AGGREGATION AND CATALYTIC PROPERTIES
Abstract:
The micellization of dilauryldimethylammonium bromide (DLDMAB) in water was studied by using surface tension measurements. The critical micellar concentration (CMC) was determined at 25°C, 32°C and 40°C and thermodynamic parameters such as the free energy of micellization (∆G°<sub>mic</sub>), enthalpy (∆H°<sub>mic</sub>), and entropy (∆S°<sub>mic</sub>) of micellization were measured. The CMC at 25°C was 4.93 x 10-5 M and the corresponding values of the thermodynamic parameters were: ∆G°<sub>mic</sub> = -5.87 kcal/mol; ∆H°<sub>mic</sub> = -1.12 kcal/mol and ∆S°<sub>mic</sub> = +16.00 e.u. Micelles of the surfactant DLDMAB act as catalysts for the alkaline hydrolysis of p-nitrophenyl diphenyl phosphate (NPDPP) with a maximum catalytic factor of approximately 120 compared to 80 for CTAB. Typical activation parameters measured for 1.00 x 10<sup>-3</sup> M surfactant and 0.005 M NaOH were: Ea = 9.7 kcal/mo/; ∆H°<sup>≠</sup> = 9.1 kcal/mol; ∆G°<sup>≠</sup> = 19.6 kcal/mol and ∆S°<sup>≠</sup> = -33.9 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 to describe the experimental results.
The micellization of dilauryldimethylammonium bromide (DLDMAB) in water was studied by using surface tension measurements. The critical micellar concentration (CMC) was determined at 25°C, 32°C and 40°C and thermodynamic parameters such as the free energy of micellization (∆G°<sub>mic</sub>), enthalpy (∆H°<sub>mic</sub>), and entropy (∆S°<sub>mic</sub>) of micellization were measured. The CMC at 25°C was 4.93 x 10-5 M and the corresponding values of the thermodynamic parameters were: ∆G°<sub>mic</sub> = -5.87 kcal/mol; ∆H°<sub>mic</sub> = -1.12 kcal/mol and ∆S°<sub>mic</sub> = +16.00 e.u. Micelles of the surfactant DLDMAB act as catalysts for the alkaline hydrolysis of p-nitrophenyl diphenyl phosphate (NPDPP) with a maximum catalytic factor of approximately 120 compared to 80 for CTAB. Typical activation parameters measured for 1.00 x 10<sup>-3</sup> M surfactant and 0.005 M NaOH were: Ea = 9.7 kcal/mo/; ∆H°<sup>≠</sup> = 9.1 kcal/mol; ∆G°<sup>≠</sup> = 19.6 kcal/mol and ∆S°<sup>≠</sup> = -33.9 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 to describe the experimental results.
DOI: 10.48141/SBJCHEM.v17.n17.2009.23_2009.pdf
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