Rheology of transient colloidal gels by Brownian dynamics computer simulation

Brownian dynamics, simulation has been used to model the dynamics and rheol ogy of transient particle colloidal gels during formation, by quenching mon odisperse attractive spherical colloidal particles from a supercritical sta te point into the vapor-liquid or vapor-solid parts of the phase diagram. C alculations were performed with particles interacting via 12:6, 24:12, and 36:18 Lennard-Jones-type interaction laws at subcritical temperatures (kT/e psilon > 0.3, where epsilon is the depth of the potential well) and low vol ume fractions (phi less than or equal to 0.2). These systems developed a ge l-like morphology during the simulation with the aggregate morphology and R heology being sensitive to the range of the attractive part of the potentia l and its underlying phase diagram. The long range 12:6 systems rapidly for med compact structures, whereas the systems generated using the shorter-ran ged 24:12 and 36:18 potentials persisted in a more diffuse network for the duration of the simulations and evolved much more slowly with time, althoug h none showed any indication of coming to a structural or rheological arres t. The rheology of these systems was characterized principally using linear stress relaxation functions computed using the Green-Kubo fluctuation form ula. An approximate direct method for computing the dynamic moduli that doe s not rely on a Fourier transformation of the stress relaxation function wa s also tested.,The rheology of many of the systems evolved with time from t he initial uniform distribution of particles, to a gel-like viscoelastic ma terial, especially for the long-range attractive interaction potentials. De spite being the most short lived, the 12:6 potential systems give the most pronounced gel-like rheological features. (C) 1999 The Society of Rheology. [S0148-6055(99)01501-1].