Estudo teórico computacional dos sistemas micelares de alquilbenzenos em diiodometano
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The surfactant-like behavior of the alkylbenzenes in diiodomethane is experimentally verified, being observed, in addition to the characteristic effects on the surface tension, evidences of clusters formation. The main goal of this work is to provide a theoretical counterpart for these systems by means of molecular dynamics simulations. Since there is no parameters for the diiodomethane molecule in any available forcefield, this molecule was parametrized using the simplex method to reproduce the density and the vaporization enthalpy. Variations in the interaction potential between the diiodomethane and the octylbenzene molecules were tested and, although there were some structural patterns similar to the micellar systems in aqueous media, the formation of well-defined micelles in this system was not observed. On the other hand, the spontaneous adsorption of both the octylbenzene and the heptadecylbenzene in the diiodomethane/vacuum interface was observed, being also prepared a compact film of heptadecylbenzene that remained stable in the nanosecond time scale. The structure and the electrostatic potential generated by these films were characterized, being observed electrostatic potential variations similar to the variations found in analogous systems in water. The potential of mean force for removing of one octylbenzene molecule from the diiodomethane/vacuum interface was calculated by means of umbrella sampling simulations and coherent values for the adsorption free energy were found.