On gelation kinetics in a system of particles with both weak and strong interactions

The kinetics of weak gelation is modelled as a system of spherical particles interacting with sticky hard-sphere pair potentials. Gradual cross-linking of primary particles to form disordered non-close-packed aggregates of greater total excluded volume than the separate non-bonded primary particles leads to a steady increase in the effective volume fraction of the sticky hard-sphere system. Characterizing the bonded aggregate structure by a single fractal dimensionality, d(f), the model predicts a time-dependent average cluster size which diverges as the system reaches the percolation threshold. The inferred gel time is shown to be rather sensitive to bonded aggregate structure as measured by the value of d(f). The model may provide a simple kinetic description of particle gel formation in real systems having a combination of weak and strong particle interactions.