Rheology of viscoelastic suspensions

Abstract

The rheology of suspensions of solid particles in viscoelastic fluids is important in many technological applications as exemplified by the processing of filled polymers e.g. injection molding, coating processes, application in food and health care products,... Consequently, considerable attention in the literature is given to the rheology of suspensions of particles. Most studies are focused on highly filled systems (typically, volume fractions greater than 10%), with polydisperse particles of irregular shapes due to their technological importance. In contrast, realtively few studies are conducted on the rheology of dilute or semi-dilute suspensions of monodisperse spheres. In the first part we elucidate the effect of viscoelasticity on the bulk rheological properties. The behavior of model suspensions composed of non Brownian, inertialess, rigid spheres immersed in Newtonian and viscoelastic matrices is investigated in the concentration range from 0 up to 10%, thus encompassing both the dilute and semidilute regimes. The data are fitted with quadratic polynomial functions of the particle volume fraction in order to compare with theoretical, empirical and experimental models. As second part, new simulation technique for suspensions in Newtonian fluids under oscillatory shear flow is presented. The cases of a single sphere and two particles are studied and discussed. Finally, the flow induced microstructure of suspensions in viscoelastic fluids is studied by rheo-optical techniques. More specifically, the flow-induced alignment of non-colloidal particles in viscoelastic fluids is investigated systematically in an attempt to quantify the alignment of the particles and correlate it with the shear rate, size of the particles and interactions with the wall.