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

通常，液体被描述为三维各向同性系统。然而，边界，如自由液体表面或固-液界面，区分空间方向并引起各向异性。这种降低的对称性可以被限制在靠近表面/界面区域的纳米尺度上，或者它可以在更大的尺度上渗透到液体中。液体中相关的有序化现象已经得到了很好的证实，最近的研究表明，近界面结构主要依赖于固体界面的化学终止。进一步证实，流动液体中的剪切可以对块体结构产生显著的影响，更显著的影响可能发生在界面上的近地表异常或不连续处，如表面滑移所证明的那样。尽管这些不连续可能具有有限的空间延伸，但它们对结构和动力学的影响可能与更大的体积相关。我们建议用表面敏感的中子和X射线散射来研究聚合物溶液中大部分未知的近表面区域的结构和动力学性质，这使得我们能够了解到到目前为止尚未探索的液体流动的时间和空间区域。

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.