Structured and viscous water in subnanometer gaps

Tai-De Li, Jianping Gao, Robert Szoszkiewicz, Uzi Landman, Elisa Riedo
2007 Physical Review B  
Direct and simultaneous measurements of the normal and lateral forces encountered by a nanosize spherical silicon tip approaching a solid surface in purified water are reported. For tip-surface distances, 0 ± 0.03 nm Ͻ d Ͻ 2 nm, experiments and grand canonical molecular-dynamics simulations find oscillatory solvation forces for hydrophilic surfaces, mica and glass, and less pronounced oscillations for a hydrophobic surface, graphite. The simulations reveal layering of the confined water density
more » ... and the development of hexagonal order in layers proximal to a quartz surface. For subnanometer hydrophilic confinement, the lateral force measurements show orders of magnitude increase of the viscosity with respect to bulk water, agreeing with a simulated sharp decrease in the diffusion constant. No viscosity increase is observed for hydrophobic surfaces.
doi:10.1103/physrevb.75.115415 fatcat:b6e23optxbfnvkjphzdqtwir4e