BIMODAL MODEL OF CONCENTRATED SUSPENSION VISCOSITY FOR DISTRIBUTED PARTICLE SIZES

A polydisperse suspension with a particle size distribution from submi crometer to hundreds of micrometers is treated as bimodal, wherein it is made up of a colloidal fine fraction and a noncolloidal coarse frac tion. According to the bimodal model, the fine fraction imparts to the suspension its non-Newtonian characteristics and behaves independentl y of the coarse fraction, whereas the coarse particles only raise the apparent viscosity through hydrodynamic interactions. It is shown that when the particle microstructure is random, the contribution to the v iscosity of the coarse fraction, which is generally polymodal, is char acterized by lubrication concepts with the maximum packing fraction ph i(m) as the scaling parameter. It is found that phi(m) is equal to the dry random packing fraction divided by a filler dilatancy factor of 1 .19. The bimodal model and lubrication concepts have also been success fully applied to bidisperse suspensions with a very large particle siz e ratio. An inverse procedure is described that makes use of the resul ts from viscosity and dry random packing measurements to divide a cont inuous size distribution into a colloidal and a noncolloidal fraction.