Molecular Features of Hydration Layers: Insights from Simulation, Microscopy, and Spectroscopy

Water molecules are orderly when stacked on a material surface in a liquid or under ambient conditions. Such a hydration layer plays a crucial role in various chemical and biological processes at interfaces. Significant gaps exist however in our understanding of the molecular structure and dynamics of a hydration layer. Atomic force microscopy (AFM) and vibrational sum frequency generation (VSFG) are widely used to probe the molecular stacking and orientation in a hydration layer. We review the molecular features of a hydration layer extracted from AFM and VSFG and how a molecular simulation can give a clear and quantitative interpretation of these experiments.