Simulations of hydration lubrication between surfaces

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Hydration lubrication describes a biologically and technically relevant range of lubrication phenomena between polar surfaces, characterized by an ultralow friction coefficient. It originates from strongly bound hydration layers formed around local surface charges. These hydration layers provide extraordinary lubrication properties that can resist also large loads. The experimental discoveries in the recent decade are still awaiting for thorough theoretical explanations and understanding. In order to illuminate the underlying mechanisms, we propose a study of the hydration lubrication phenomenon in terms of atomistic modeling. We plan to combine non-equilibrium flow as well equilibrium simulations with our novel techniques that enable to determine the exact hydration level at prescribed water chemical potential. In the first part we consider simple planar surfaces with controllable degrees of polarity and stiffness, which allows for a systematic study of the fundamental principles of friction forces. We proceed the study with experimentally relevant phospholipid membranes in fluid as well as gel phases. We intend to complement the results by investigating the underlying microscopic mechanisms based on hydrogen bonding dynamics, water order parameters, and membrane structure.