(303b) Dynamic Model of a Water Nanodroplet Under a Transmission Electron Microscope

We report and investigate an experimental phenomenon of torus-shaped water nanodroplets sliding on a hydrophilic substrate in a cyclical stick-slip fashion under a transmission electron microscope. Using continuum long wave theory, we propose a physical model for the stress imposed by electrical charges and explain how the non-uniform distribution of charges on the surface of a sufficiently pinned convex drop could eventually lead to a deformation into a toroidal shaped drop. The depression at the drop center is shown to depend on the balance between the electrostatic stress and the surface tension of the drop. On the other hand, the lateral component of the unbalanced electrostatic stress creates a lateral driving force, which when sufficiently large, could overcome surface heterogeneities in the substrate disjoining pressure, such that the drop slides on the substrate surface through a cyclical stick-slip motion. The present model predicts step-like dynamics in drop displacement and surface area jumps, both qualitatively consistent with experimental observations.