Rheology of concentrated disperse systems III. General features of the proposed non-newtonian model. Comparison with experimental data
Tóm tắt
A non-newtonian viscosity equation
$$\eta _r = (1 - \tfrac{1}{2} \cdot \tilde k\phi )^{ - 2} $$
whereφ is the volume concentration and
$$\tilde k = (k_0 + k_\infty \dot \gamma _r^p )/(1 + \dot \gamma _r^p )$$
is an intrinsic viscosity, function of a relative shear rate
$$\dot \gamma _r = \dot \gamma /\dot \gamma _c , k_0 , k_\infty $$
and
$$\dot \gamma _c $$
being structural parameters, has been proposed in a previous paper (1). From empirical grounds, the valuep = 1/2 holds for a large class of systems, like suspensions of rodand disc-shaped particles. In the high shear rate limit, aCasson law-type is recovered and discussed, especially the concentration dependence of the yield stress. However, the latter disappears in the low shear limit, and must be considered as a pseudo-yield stress. Good agreement is found in this low shear limit with some theoretical results ofBueche for polymers. More generally, the viscosity equation displays pseudo-plastic behaviour and fitting it on experimental data allows the determination of the structural parameters. Some examples (especially Red Blood Cell suspensions and Blood) are studied and support the model. Nevertheless, for spherical particle suspensions, the best fitting is reached forp = 1. Accurate values of particle diameters can be deduced from the structural parameter
$$\dot \gamma _c $$
, in this case.
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