Particle shape and suspension rheology of short-fiber systems

The effective viscosity of short-fiber suspensions is studied from a theoretical and experimental point of view. The theory of dilute suspensions with elongated particles is briefly summarized and explicit formulae for the dependence of the intrinsic viscosity on the particle shape (aspect ratio) are given in a form that should be useful for practical purposes. Concentration regimes, the influence of Brownian motion and sedimentation kinetics are mentioned. The effective viscosity of suspensions of two polydisperse wollastonites with significantly different average aspect ratios (approximately 5 and 16, respectively) is measured in dependence of the solids volume fraction and fitted with power-law models (Krieger and Maron–Pierce relations). It is shown that the intrinsic viscosity determined is higher than theoretically predicted via the Brenner formula, while the critical volume fraction is lower than predicted by the empirical Kitano relation. Possible reasons for these discrepancies, common to most real polydisperse systems, are discussed.