By monitoring the thermal noise of a vertically oriented micromechanical force sensor, we detect the viscoelastic response to shear for water in a subnanometer confinement. Measurements in pure water as well as under acidic and high-ionic-strength conditions relate this response to the effect of surface-adsorbed cations, which, because of their hydration, act as pinning centers restricting the mobility of the confined water molecules.
© 2011 American Chemical Society