Shear - induced aggregation and break up of fibril clusters close to the percolation concentration

Structural changes of complex fluids under steady shear flow were investigated for different type of materials, such as suspensions, associating polymers and polymer solutions [1, 2, 3, 4, 5, 6]. Under specific conditions, depending on the material, a shear-thickening regime is observed followed by shear-thinning behaviour [3, 4, 6]. Shear-thickening is often the result of shear-induced formation of intermolecular structures (clusters), leading to an increase in the effective volume fraction [1, 2, 3, 5, 7]. Clusters convected by shear flow may aggregate upon contact, due to attractive interactions of particles on the periphery of the clusters. Cluster–cluster collisions that occur along the streamlines of shear flow lead to the formation of larger clusters [7]. In polymer solutions, the size of these clusters depends upon the concentration [4]. Shear-induced stretching of the structures can also contribute to a shear-thickening effect [4, 8, 9]. Increasing the shear rate increases the stress on these structures, and once a critical stress is exceeded, they break up, giving rise to shear-thinning behaviour [3, 4, 6]. Cecile Veerman Leonard M. C. Sagis Paul Venema Erik van der Linden Shear-induced aggregation and break up of fibril clusters close to the percolation concentration