Estudo em simulação Monte Carlo de sistemas coloidais com descontinuidade dielétrica

Abstract

In this work, extensive Monte Carlo simulations in the canonical ensemble have been performed to study the equilibrium properties of charged colloidal systems, where the colloidal particle has a dielectric constant different from the surrounding medium. First, we review the Poisson-Boltzmann (PB) theory, used in the restricted primitive model of a Wigner-Seitz (WS) cell without dielectric discontinuity, in order to derive the electric field and microion density profiles around the macromolecule. We compare the integrated and effective charges calculated by using PB and Monte Carlo simulations, in order to establish where the PB breaks down. After that, we review the theory for dielectric spheres, describing how the dielectric discontinuity at the surface of colloidal particle is related to the polarization-induced charges. The method of Kelvin images and counterimages charges is used to solve the electrostatic problem, in order to obtain a simplifying approximation for the electrostatic interacting energy from a computational point of view. This method is then investigated for a colloidal particle inside a WS cell by using Monte Carlo simulations for several scenarios: in both salt-free and monovalent and divalent salty environments, and varying the colloidal charge. We compare our results with previous formulations, specially the counterions and coions profiles, zeta potential and effective charge. Our results suggest that polarization-induced charges decreases the renormalization of charge in a colloidal system.