Brownian Dynamics Simulations of Aggregation and Gel Formation in Lennard-Jones Fluids

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Abstract
We report structural, thermodynamic and rheological properties of a three dimensional Lennard-Jones fluid as it is quenched, at various densities, from above the critical temperature into the two phase gas-liquid 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 peak heights in the radial distribution function, with the formation of a percolating network at low temperature (T∼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 viscosity and decreasing self-diffusion coefficient during the quench. The shear stress time correlation functions exhibit stretched exponential behaviour at long time. In fact, limiting long time relaxation is dominated by a single relaxation time, which is evident in excellent Maxwell-like visnoelastic behaviour in the low frequency region of the dynamic moduli.