Auto-organização e dinâmica de um sistema coloidal binário

Abstract

In this work we investigate the structural and dynamical properties of a system of classical particles, with opposite charges, under the action of a parabolic confinement (quasiunidimensional confinement), wich interact by Yukawa Potential and a soft-core repulsive potential, in function of system density and stoichiometry. The model here proposed is suitable for the study of colloidal particles (solute) stabilized in a liquid medium (solvent). In the first part of dissertation, we investigates the minimum energy configurations of the system (temperature T = 0) through computational simulations (Monte Carlo) method and analytical calculations. Despite the non-triviality of the interaction potential between charges, we noted that it is possible to form simple stable configurations (alloys) along the channel, in which the particles get self-organized in linear chains along the parabolic channel. Depending on the density the equilibrium configurations can be interpreted as chains of particles or as chains of electric dipoles. We study the mechanical vibrations of these alloys (in the case of 1 and 2 chains structures), where it is possible to prove the stability of these configurations. Phonon spectrum of the 1- chain structure reveals the presence of gap’s through which it is not possible the propagation of a wave. In this case, the structure of 1 chain can be thought as a mechanical wave filter. Waves with frequencies in the range associated with the ”gap”are not possible to propagate along the structure. In the second part of this work, we study particles diffusion through computer simulation using Brownian Dynamics method. Diffusion is studied as a function of range and intensity of interaction between particles and in function of temperature. The intensity of the interaction is examined by density variation. All these parameters have considerable influence on the diffusion process. In general, we note that the increase in density decreases the exponent that characterizes the diffusive process, generating different values from those known from the literature. Increased stoichiometry also contributes to this behavior, once the particles of bigger charge have a larger radius, and thus affect more particles in its vicinity, modifying the diffusive process locally. The influence of temperature depends on the configuration. However, a very interesting fact is that decrease in temperature process generates a superdiffusive behavior in the intermediate regime. This is a new fact in colloidal systems and is associated with competitive potential (repulsion/attraction) characteristic of interaction between system charges.