PHYSICAL CHEMICAL STUDIES OF THE SURFACTANT DILAURYLDIMETHYLAMMONIUM BROMIDE (DLDMAB): AGGREGATION AND CATALYTIC PROPERTIES
Abstract:
<p align="justify"> 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. </p>
<p align="justify"> 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. </p>
DOI: 10.48141/SBJCHEM.v17.n17.2009.23_2009.pdf
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