BROWNIAN DYNAMICS SIMULATIONS OF LENNARD-JONES GAS LIQUID PHASE-SEPARATION AND ITS RELEVANCE TO GEL FORMATION/

Brownian dynamics computer simulations have been used to follow the ph ase separation behaviour of model adhesive colloidal systems quenched in temperature from a supercritical state into the two-phase coexisten ce region, CR, of the phase diagram. The systems studied consisted of monodisperse spherical particles interacting through either 12-6, 24-1 2 or 36-18 pair potentials. Systems quenched to state points just insi de the two-phase boundary initially exhibit negligible domain growth o r a period of 'latency' before slow decomposition, a feature associate d with phase separation by nucleation. Systems quenched further into t he two-phase region are characterised by immediate decomposition and m ore rapid growth of a characteristic length scale, behaviour character istic of phase separation via a spinodal decomposition mechanism. Both domain size and peak height followed a power law growth with time ove r a period of the separation and some systems exhibit dynamic scaling of the structure factors. For systems at a volume fraction in excess o f ca. 0.1 percolating interconnecting networks formed which manifested gel-like properties such as an increasing infinite frequency shear mo dulus, the appearance of a low-frequency shear modulus and more pronou nced power-law behaviour of the stress time autocorrelation functions. The LJ clusters consist of compact regions separated by thin branches , whereas the shorter ranged potentials formed more tenuous gel-like s tructures. Phase separation was slower for the shorter range attractiv e potentials.