Out Of Equilibrium Anomalous Elastic Response Of A Water Nano-Meniscus

We report the observation of a transition in the dynamical properties of water nano-meniscus which dramatically changes when probed at different time scales. Using an AFM mode that we name Force Feedback Microscopy, we observe this change in the simultaneous measurements, at different frequencies, of the stiffness G' (N/m), the dissipative coefficient G'' (kg/s) together with the static force. At low frequency we observe a negative stiffness as expected for capillary forces. As the measuring time approaches the microsecond, the dynamic response exhibits a transition toward a very large positive stiffness. When evaporation and condensation gradually lose efficiency, the contact line progressively becomes immobile. This transition is essentially controlled by variations of Laplace pressure. (c) 2015 AIP Publishing LLC.