RHEOLOGICAL PROPERTIES OF DISPERSE SYSTEMS OF SPHERICAL-PARTICLES IN POLYSTYRENE SOLUTION AT LONG TIME-SCALES

In the reported experiments the dynamic and steady flow properties of disperse systems of styrene-divinylbenzene copolymer particles in a PS solution have been measured over wide ranges of frequency, shear rate, and strain amplitude by means of a cone-and-plate type rheometer. These systems have been shown to exhibit the Newtonian behavior at extremely low rates of shear, that is, the apparent viscosity is approximately constant. They also show linear viscoelastic behavior at strain amplitudes less than 0. 5%, but striking nonlinearities at larger strains. However, at very long time-scales, these systems are linearly viscoelastic and independent of the strain amplitude. The nonlinear viscoelastic functions G//1 prime and G//1 double prime decrease with increasing strain amplitude, but they are almost independent of strain for strains larger than 50%, over the entire frequency range. The relaxation spectra for these disperse systems consist of two parts: one is the box type portion in the long time-scale region, where the intensity is very sensitive to strain; the other appears in the short time-scale region and is not sensitive to strain. On the basis of these results, a new concept for the yield stress of disperse systems is proposed and discussed.