Computer simulation of polymer brushes under shear

Recently two different methods were used to simulate the stationary propert ies of polymer brushes under strong shear: stochastic dynamics of a multi-c hain brush model, and self-consistent Brownian dynamics of a one-chain mode l. The former explicitly describes volume interactions (VI) between polymer segments but does not take into account hydrodynamic interactions (HI) ins ide the brush. In the latter the self-consistent molecular field method has been chosen to calculate VI, and HI were accounted for using the Brinkman equation. Despite a significant difference between models a collapse of the brush under shear was observed in both studies. In particular, the density profile changes from parabolic to step-like and the free ends of the chain s become concentrated in a narrow region at the periphery of the brush. How ever, when HI are taken into account much higher shear rates are necessary to attain the same brush deformation because the shear flow only slightly p enetrates into the brush in contrast to the free-draining case. The inner b rush structure is also found to be different for the two models. In the fir st model all chains are inclined approximately at the same angle when shear is applied. In the second model chains with the free ends found in the inn er sublayer of the brush do not feel the flow at all whereas those in the u pper sublayer are stretched and inclined by the flow.