The yield stress of concentrated flocculated suspensions of size distributed particles

An investigation of shear yield stress is made on well-characterized alumin a suspensions of different distributed particle sizes at the vicinity of th e particle isoelectric point (IEP) across a wide range of volume fractions. Experimental results are compared with recently developed models [Kapur et al. (1997); Scales et al. (1997)] and structural effects on the yield stre ss are examined. The models predict the magnitude order of the yield stress below a volume fraction of approximately 0.42, suggesting that interpartic le forces play a dominant role in determining the network strength in this concentration region. Deviations between experimental results and theoretic al predictions are explained in terms of structural effects being controlle d by a competition between weak particle-particle linkages and geometric re sistance on the network strength. At higher volume fraction, the effect of geometric resistance on the deformation of suspensions becomes more pronoun ced. A number of models for the yield stress of size distributed suspension s an then proposed. Results suggest that the effect of polydispersity of pa rticles on the yield stress of suspensions can be well characterized by a s urface area average diameter and the broad size distributed suspension exhi bits a higher yield stress than the narrow size distributed suspension of t he same volume average diameter. (C) 1999 The Society of Rheology. [S0148-6 055(99)00303-X].