BROWNIAN DYNAMICS SIMULATIONS OF AGGREGATION AND GEL FORMATION IN LENNARD-JONES FLUIDS

We report structural, thermodynamic and rheological properties of a th ree dimensional Lennard-Jones fluid as it is quenched, at various dens ities, from above the critical temperature into the two phase gas-liqu id coexistence region. The structural and dynamical behaviour observed has many similarities with a sol-gel transition. There is a growth in cluster size for the spherical particles, evident also in growing pea k heights in the radial distribution Function, with the formation of a percolating network at low temperature (T similar to 0.2-0.3) and at sufficiently high volume fractions (>0.1). This change is also marked by diverging structural relaxation times, manifest in an increasing vi scosity and decreasing self-diffusion coefficient during the quench. T he shear stress time correlation functions exhibit stretched exponenti al behaviour at long time. In fact, limiting long time relaxation is d ominated by a single relaxation time, which is evident in excellent Ma xwell-like viscoelastic behaviour in the low Frequency region of the d ynamic moduli.