Water in confined geometries

Studies of water in confined geometries are of great relevance, since most water on the Earth surface is confined, in rocks, cells, food and so on. It is however yet unknown to what extent present knowledge about bulk water can help in understanding confined water behavior and vice versa, and to what extent the physics and chemistry of the confining medium affect the properties of bulk water. In other words, if there are any characteristics common to all confined waters. Here we present a structural study of water under several quite distinct confining media, showing that independently of the nature and shape of the substrate, the first water layers in the vicinity of the substrate surface are denser than those far away from it and that the average water density under confinement is lower than in bulk at the same temperature and pressure conditions. On the other hand, the extent of the structural disturbance to water structure, due to confinement, seems the result of a complex interplay between interaction forces and size