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Polymer Brush Collapse under Shear Flow

Polymer Brush Collapse under Shear Flow

Published in Macromolecules

Shear responsive surfaces offer potential advances in a number of applications. Surface functionalization using polymer brushes is one route to such properties, particularly in the case of entangled polymers. In this article, we report on neutron reflectometry measurements of polymer brushes (PS) in contact with a solution entangled polymer solutions performed under controlled shear as well as coarse-grained computer simulations corresponding to these interfaces. When the solution, in contact with the brush is sheared, we show a reversible and reproducible collapse of the brushes. Moreover, we showed an increasing of the collapse with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are mainly governed by the free chains in solution rather than the brush itself, within the range of parameters examined. A scaling law for the collapse as a function of the Weissenberg number is proposed. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors and as a way to dynamically control surface friction and adhesion.

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