Out of equilibrium anomalous elastic response of a water nano-meniscus

TL;DR

This study reveals a transition in the elastic response of water nano-menisci from negative to large positive stiffness at microsecond time scales, driven by changes in contact line mobility and Laplace pressure.

Contribution

We demonstrate a novel transition in nano-meniscus elasticity at different time scales using Force Feedback Microscopy, highlighting the dynamic change from negative to positive stiffness.

Findings

Negative stiffness observed at low frequencies due to capillary forces.

Transition to large positive stiffness near microsecond time scales.

Contact line becomes immobile as evaporation and condensation effects diminish.

Abstract

We report the observation of a transition in the dynamical properties of water nano-menicus which dramatically change when probed at different time scales. Using a 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/sec) 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.