Rheology of “Wet” Polymer Brushes via Brownian Dynamics Simulation: Steady vs Oscillatory Shear

The rheology of solvent-filled polymer brushes under steady and oscillatory shear is studied by Brownian dynamics simulation. The flow field is solved self-consistently with the polymer dynamics. We find that under steady flow the brushes are shear thinning in both normal forces and shear viscosity. During oscillatory flow, extreme shear thickening occurs when the ratio of the Weissenberg number to the dimensonless flow frequency Wi/ω≈3. Shear-induced diffusion is shown to create this thickening. These findings serve to explain the recent measurements made by Klein et al. [Nature 352, 143 (1991); 370, 634 (1994); Discuss Faraday Soc. 98, 173 (1994)].