title: Direct observation of stick-slip movements of water nanodroplets induced by an electron beam.
abstract: Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface. At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10- to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps. We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state.
authors.affiliation: MechanoBiology Institute-Singapore, National University of Singapore, 5A Engineering Drive 1, Singapore 117411.
authors.forename: Utkur M
authors.initials: UM
authors.lastname: Mirsaidov
authors.forename: Haimei
authors.initials: H
authors.lastname: Zheng
authors.forename: Dipanjan
authors.initials: D
authors.lastname: Bhattacharya
authors.forename: Yosune
authors.initials: Y
authors.lastname: Casana
authors.forename: Paul
authors.initials: P
authors.lastname: Matsudaira
mesh_terms: D000465:Algorithms; D004583:Electrons; D057927:Hydrophobic and Hydrophilic Interactions; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D055672:Static Electricity; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water