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Saphiannikova, M. ; Neelov, I; Pryamitsyn, V; Darinskii, AA; Sundholm, F;
Computer simulation of polymer brushes under shear

Recently two different methods were used to simulate the stationary properties of polymer brushes under strong shear: stochastic dynamics of a multi-chain brush model, and self-consistent Brownian dynamics of a one-chain model. The former explicitly describes volume interactions (VI) between polymer segments but does not take into account hydrodynamic interactions (HI) inside 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 chains become concentrated in a narrow region at the periphery of the brush. However, when HI are taken into account much higher shear rates are necessary to attain the same brush deformation because the shear flow only slightly penetrates into the brush in contrast to the free-draining case. The inner brush structure is also found to be different for the two models. In the first 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 inner sublayer of the brush do not feel the flow at all whereas those in the upper sublayer are stretched and inclined by the flow.

Rheologica Acta 39, 469-475


Erschienen am
October 2000