Brownian dynamics simulation of dense binary colloidal mixtures. I. Structural evolution and dynamics.

Abstract

We have carried out Brownian dynamics simulations of binary mixtures of charged colloidal suspensions of two different diameter particles with varying volume fractions \ensuremath{\varphi} and charged impurity concentrations ${\mathit{n}}_{\mathit{i}}$. For a given \ensuremath{\varphi}, the effective temperature is lowered in many steps by reducing ${\mathit{n}}_{\mathit{i}}$ to see how structure and dynamics evolve. The structural quantities studied are the partial and total pair distribution functions g(r), the static structure factors, the time average g(r\ifmmode\bar\else\textasciimacron\fi{}), and the Wendt-Abraham parameter. The dynamic quantity is the temporal evolution of the total mean-squared displacement (MSD). All these parameters show that by lowering the effective temperature at \ensuremath{\varphi}=0.2, liquid freezes into a body-centered-cubic crystal whereas at \ensuremath{\varphi}=0.3, a glassy state is formed. The MSD at intermediate times shows significant subdiffusive behavior whose time span increases with a reduction in the effective temperature. The mean-squared displacements for the supercooled liquid with \ensuremath{\varphi}=0.3 show staircase behavior, indicating a strongly cooperative jump motion of the particles.