Shear-induced gel widening and solvent release in the vorticity direction

Shear-induced gel widening and a new way of solvent release are observed using a counter-rotating rheo-optical tool. It occurs in the vorticity direction, perpendicular to shear flow, together with gel particle deformation and solvent release in the flow direction. The gel particles used are polyelectrolyte networks swollen in aqueous solutions of hydroxypropylcellulose and placed in a hydrophobic matrix. As soon as the complex modulus of the matrix becomes larger than the shear modulus of the swollen gel, the gel widens, releases solvent in the vorticity direction and then solvent is detached and flows away. The cycle of solvent release/detachment can be repeated several times. This Gel behaviour under shear seems to be governed by the same mechanism as liquid droplet widening in a visco-elastic liquid. (c) 2005 Elsevier B.V. All rights reserved.