Viscoelastic Behavior of Bimodal Ideal Suspensions.

Abstract

We examined the viscoelastic behavior of ideal suspensioncs consisting of spherical particles with hard-core potential between them. Unimodal ideal suspensions showed viscoelasticity with relaxation times proportional to the cube of the particulate radius. Bimodal ideal suspensions with a ratio of particulate radii below 4 had viscoelastic properties similar to those of unimodal ideal suspensions, of which the relaxation times were proportional to the product of the average particulate radius and the average of the particulate radius squared. However, bimodal ideal suspensions with a ratio greater than 5 showed two distinct relaxation times. The fast relaxation time was related to the motion of smaller particles and the slow relaxation time was related to that of larger particles. The ratio of 5 should be a criterion whether or not the motion of two types of particles can be averaged into one set of modes with an average relaxation time. A model for predicting frequency dependency of storage and loss moduli for bimodal ideal suspensions with the ratio of particle radii greater than 5 was proposed. Agreement between the frequency dependency of the model and the experimental data was quite good. Moreover, essential rheological parameters such as zero-shear and high frequency limiting viscosities were reasonably predicted by the model.