Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

• Published in: Proceedings of the National Academy of Sciences - PNAS 2012-05, Vol.109 (19), p.7187-7190
• Main Authors: Mirsaidov, Utkur M., Zheng, Haimei, Bhattacharya, Dipanjan, Casana, Yosune, Matsudaira, Paul
• Format: Article
• Language: English
• Subjects: Algorithms; Average speed; Deformation; Electron beams; Electrons; Gas solid interfaces; Hydrophobic and Hydrophilic Interactions; Kinetics; Liquids; Microscopy, Electron, Transmission; Models, Chemical; Molecules; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanotechnology; Particle Size; Physical Sciences; Static Electricity; Surface energy; Surface Properties; Temperature; Thermodynamics; Transmission electron microscopy; Velocity; Water; Water - chemistry
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1200457109

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 non wetting, 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.