2 research outputs found
Polymer brush collapse under shear flow
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
Probing the dynamics of high-viscosity entangled polymers under shear using Neutron Spin Echo spectroscopy
Neutron Spin Echo spectroscopy provides unique insight into molecular and submolecular dynamics as well as intra-and inter-molecular interactions in soft matter. These dynamics may change drastically under shear flow. In particular in polymer physics a stress plateau is observed, which might be explained by an entanglement-disentanglement transition. However, such a transition is difficult to identify directly by experiments. Neutron Spin Echo has been proven to provide information about entanglement length and degree by probing the local dynamics of the polymer chains. Combining shear experiments and neutron spin echo is challenging since, first the beam polarisation has to be preserved during scattering and second, Doppler scattered neutrons may cause inelastic scattering. In this paper we present a new shear device adapted for these needs. We demonstrate that a high beam polarisation can be preserved and present first data on an entangled polymer solution under shear. To complement the experiments on the dynamics we present novel SANS data revealing shear-induced conformational changes in highly entangled polymers