The Rheology of Suspensions

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Abstract
The rheological properties of concentrated suspensions of sized glass spheres in an equal‐density medium has been investigated with the rotational viscosimeter. It has been found that the variation of fluidity with rate of shear can be expressed satisfactorily by a form of an expression suggested by Reiner relating the fluidity to the shearing stress, the fluidity at rest, and the fluidity at infinite shearing stress. It is also shown that values of the apparent fluidity are influenced by the time of shearing, the aging of the suspensions, and temperature effect attributed to the work of shearing. The viscosity of suspensions of sized spheres at concentrations as great as 55 volume percent solids may be satisfactorily represented by either the relation of Mooney or of Maron, Madow, and Krieger; the identity of their relations is also shown. The constants for the equation relating viscosity and concentration are shown to be in satisfactory agreement with those predicted by Mooney. Constants for the viscosity‐concentration equation are also given for several examples of experimental work selected from the literature; the form of equation proposed by Mooney relating viscosity and concentration is generally useful though the constants may not agree with the predicted values. It has been found that the apparent fluidity of the glass bead suspensions decreases with an increase in particle diameter when the suspending fluid is zinc bromide in aqueous glycerol though the viscosity is independent of particle diameter when the suspending fluid is the nonaqueous mixture of ethylene tetrabromide and diethylene glycol. The viscosity of a bimodal system of glass beads was shown to decrease very significantly as the bulk density was increased by packing progressively smaller spheres into the interstices of the larger spheres of the bimodal system, in qualitative agreement with a relation proposed by Mooney.