  Shear responsive surfaces offer potential advances in a number of
applications. Surface functionalisation using polymer brushes is one route to
such properties, particularly in the case of entangled polymers. We report on
neutron reflectometry measurements of polymer brushes in entangled polymer
solutions performed under controlled shear, as well as coarse-grained computer
simulations corresponding to these interfaces. Here we show a reversible and
reproducible collapse of the brushes, increasing 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 governed by the free chains in solution rather than the brush itself,
within the range of parameters examined. 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.
