# Simple heuristic for the viscosity of polydisperse hard spheres

Spheres crowd around each other in a manner that depends on their size distribution. We give a simple way to estimate the packing fraction.

*Journal of Chemical Physics* 141, 214503 (2014)

We build on the work of Mooney [Colloids Sci. 6, 162 (1951)] to obtain an heuristic analytic approximation to the viscosity of a suspension any size distribution of hard spheres in a Newtonian solvent. The result agrees reasonably well with rheological data on monodispserse and bidisperse hard spheres, and also provides an approximation to the random close packing fraction of polydisperse spheres. The implied packing fraction is less accurate than that obtained by Farr and Groot [J. Chem. Phys. 131(24), 244104 (2009)], but has the advantage of being quick and simple to evaluate.

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