Depletion and fines effects on transport in hard-sphere colloids

The effect of depletion forces induced by the presence of much smaller B spheres (diameter ratio 10/1) in dense hard A spheres has been investigated. Simulations for systems of 10(4) spheres with mole fraction of larger spheres x(A) = 0.05 and with total sphere volume fraction from 0.35 to 0.655 have been carried out. The depletion force steeply increases in the A-A pair distribution function at contact, and creates a lower first coordination and more open network A-structures. There is no evidence of demixing. It is found that in the amorphous solid region there is an enhanced diffusive mobility of the larger spheres, relative to that of pure spheres, at the same densification rates. This observation resembles the fines effect that occurs in colloidal suspensions and granular fluids.