Irving Langmuir Award in Chemical Physics (2021): Confining water: from biolubrication to nano-cavitation*

The persistent fluidity of water when confined down to sub-nanometer films between solid surfaces [1], which is in striking contrast to non-polar liquids whose viscosity diverges when so confined [2], extends also to water confined to hydration layers [3]. In such cases the tenacious attachment of the water of hydration to the charges it surrounds, together with its fluidity, act as a ‘molecular ball bearing’ under confinement and shear, and thus constitute remarkable lubrication vectors, particularly in aqueous and biological environments [4-6]. Such hydration lubrication plays a crucial role in biolubrication and homeostasis of human tissues that slide past each other, especially in joints [7] and biomedical devices [8]. A very different behavior is seen when the confining surfaces are highly hydrophobic; when such surfaces approach across water, nano-cavities nucleate spontaneously between them and expand rapidly before collapsing. This effect may account for the long-known but still puzzling observations of long-ranged attraction between such surfaces [9].

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