(513b) On the Extensional Rheology of a Particle-Laden Viscoelastic Solution

Anika Jain, J. Einarsson, Eric S.G. Shaqfeh, Department of Chemical Engineering, Stanford University, Stanford, CA

Nicolas J. Alvarez, Zachary R. Hinton, Department of Chemical and Biological Engineering, Drexel University, Philadelphia, PA

Previous studies on shear flows have shown that the effective shear viscosity of particle laden viscoelastic solutions demonstrates shear thickening even at small volume fractions in contrast to the shear thinning, particle free fluid [1] [2]. This thickening is created by increasing particle-induced fluid stress in the fluid surrounding the particles which offsets a reduction in the stresslet contribution to the average shear stress. Since the particle-induced fluid stress is a nonlinear function of flow type, the conclusions from studies on shear flow do not immediately allow prediction of the material properties for other linear flows. We employ the recently developed mathematical and computational tools to understand the extensional rheology of viscoelastic suspensions. Extensional flow is of primary importance in molding, film blowing and fiber drawing applications. We therefore describe a theoretical, computational and experimental examination of the effective extensional viscosity of a particle laden Boger fluid at small and moderate particle volume fraction. The results for numerical calculation for the effective extensional viscosity for single spherical particles (i.e. in the dilute limit) as a function of strain and strain rate (i.e. Deborah number) will be presented for the Oldroyd B, FENE-P and Giesekus models. The results are compared to theories valid for small Deborah number [3]as well as a new theory valid for small strain. We compare these predictions to fiber stretching rheometry experiments up to volume fractions of 25% particle loading.