Nanoscale discontinuities at the boundary of flowing liquids: a look into structure

Abstract

When downsizing technology, confinement and interface effects become enormouslyimportant. Shear imposes additional anisotropy on a liquid. This may induceinhomogeneities, which may have their origin close to the solid interface. For advancingthe understanding of flow, information on structures on all length scales and inparticular close to the solid interface is indispensable. Neutron scattering offers anexcellent tool to contribute in this context. In this work, surface sensitive scatteringtechniques were used to resolve the structure of liquids under flow in the vicinity of asolid interface. Our results are summarized as follows. First, for a Newtonianliquid we report a depletion distance on the order of nanometers which is fartoo small to explain the amount of surface slip, on the order of micrometers,found by complementary techniques. Second, for a grafted polymer brush we findno entanglement–disentanglement transition under shear but the grafted filmgets ripped off the surface. Third, by evaluating the local structure factor of amicellar solution close to the solid interface it turns out that the degree of orderand local relaxation depends critically on the surface energy of the solid surface.