Yasuoka Laboratory



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講師Dr. Nikolai Volkov (St Petersburg State University, Russia)
題目Molecular dynamics simulations of ionic micellar solutions: diffusion, structure, and kinetics
日時2016年10月7日(Fri) 13:00〜
場所Seminar Room 3(Room 203), Building 14th, Yagami Campus, Keio University
概要Various multi-scaled kinetic phenomena in micellar solutions are determined by diffusivities of micelles, premicellar aggregates, surface-active ions, counterions, and coions [1-4]. However, even incontemporary DLS, SANS and SAXS experiments, it is practically impossible to distinguish between the aggregates with dispersed aggregation numbers and, consequently, to study them separately. Fortunately, molecular dynamics (MD) simulation allows one to examine transport and structural properties of individual surfactant aggregates with arbitrary aggregation numbers [5,6]. We used all-atom MD to study the details of micellization in sodium dodecyl sulphate (SDS) aqueous solution, starting from the surfactant molecules uniformly distributed in the simulation cell and finishing with formation of small short-lived aggregates and their subsequent fusion into larger quasi-stable aggregates. The all-atom simulations of SDS solutions, both salt-free (at several total surfactant concentrations) and with added electrolytes (NaCl, CaCl2), were carried out using CHARMM36 force field and MDynaMix package [7]. Structural, transport and kinetic properties of SDS solution were examined. The equilibrium micellar structures were characterized by the aggregation numbers, radial distribution functions, and the potentials of mean force. The interactions of premicellar aggregates with the water molecules, i.e. wetting, and with Na+ and Ca2+ counterions, i.e. counterion binding, were evaluated. The diffusivities of aggregates with different aggregation numbers, coions, counterions, and water molecules were found. The kinetics of aggregation of surface-active ions was studied at different total surfactant concentrations. The work was supported by the Russian Science Foundation (grant 14-13-00112).