Dynamics of water in complex environments, bridging the gap between molecular and mesoscopic interfaces
- Damien Laage (Ecole Normale Supérieure, PSL Univ., Sorbonne Univ., CNRS, France)
- Ward H. Thompson (University of Kansas, Lawrence, USA)
- Hilton de Aguiar (Ecole Normale Supérieure/Paris, France)
Water is the most ubiquitous liquid in our environment. However, water is rarely found as a neat liquid and is instead usually in contact with a broad range of solutes and interfaces. This includes biomolecules and ions in biological contexts, water-mineral interfaces in geochemistry, water-air surfaces in atmospheric chemistry, water-metal interfaces for corrosion, and confined within porous materials for technological applications.
A central question is thus: What is the impact of these interfaces on the properties of water, and especially on water dynamics? In the past few years new fundamental questions regarding the effects of solutes and interfaces on the dynamics of water have arisen and despite numerous studies, no consensus has developed. The workshop will focus on three in particular.
First, what is the physical origin of the effect of an interface on water dynamics? This requires elucidation of the respective roles of the interface features (e.g., topography vs. chemical functionality, entropy vs. enthalpy). This understanding is necessary to explain the different effects of an interface on the various types of water molecular motions probed experimentally (e.g., single molecule vs. collective). Given the wide gamut of aqueous interfaces, another major goal will be to identify the common features in the effects induced by small solutes and extended mesoscopic interfaces, thus bridging multiple lengthscales, and determine whether the same molecular mechanisms are involved.
Second, what is the magnitude and spatial range of the effect of an interface on water dynamics? The origin of some very slow relaxation timescales found next to some interfaces, e.g., reverse micelles, remains unclear. This has major consequences in biological contexts, where it has been suggested that water behaves as “biological water,” a wholly separate entity, for which “...pure water, in many cases, ceases to be a guide in the understanding...” of its properties. However, this view has been recently challenged.[1,7]
Third, how do the different water dynamical properties at an interface impact processes such as chemical processes? It is important to understand how the modified water dynamics in the vicinity of solutes and interfaces determine the local transport properties, solvent rearrangements involved in chemical reactions, and vibrational energy flow.
In addition to these questions about physical behavior, additional methodological challenges have to be met, for both theoreticians and experimentalists, that can only be accomplished via collaboration between the two.
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