Nanoscale Discontinuities at the Boundary of Flowing Liquids: a Look into Structure and Dynamics

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Usually liquids are characterized as 3D isotropic systems. However a boundary, like the free liquid surface or a solid-liquid interface, distinguishes a spatial direction and induces anisotropy. This reduced symmetry may be limited to a nanosize length scale next to the surface/interface region or it may penetrate into the liquid on a much larger length scale. Related ordering phenomena in liquids are well established, and more recently it was shown that near-interface structures depend crucially on the chemical termination of the solid boundary. It is further established that shear in flowing liquids may have a pronounced influence on bulk structures, and more dramatic effects may occur as near-surface anomalies or discontinuities at interfaces as evidenced through surface slip. Although these discontinuities may have a limited spatial extension, there consequences on structure and dynamics may be relevant for much larger volumes. We propose to study both the structural and dynamical properties of the largely unknown near-surface regions in polymer solutions by surface sensitive neutron and x-ray scattering which allow to access a so far unexplored time and spatial regime of flowing liquids.