Dynamics of nm-size droplets of water at the confined-bulk transition
We are able to form and then image 10-100 nm diameter droplets of water on a silicon nitride surface by irradiating a 100-200 nm thick column of bulk water with a focussed electron beam of a transmission electron microscope. The bulk water is enclosed in a liquid cell microfabricated from silicon with thin silicon nitride windows and sealed from the vacuum of the TEM. The droplets form by a process that resembles spinodal decomposition. Various types of electron-beam dependent dynamics are observed including droplet movement, collision and merging of droplets, spontaneous and reversible appearance and disappearance of droplets. These movements take place on silicon nitride rendered hydrophilic by glow discharge. The liquid cells were developed to image protein assemblies in room temperature liquid water. We have imaged a crystalline bundle of actin filaments, the acrosomal process, at 120 kV to a resolution of 2.7 nm. Surprisingly, radiation damage by the electron beam is less in room temperature bulk water than in vitreous ice cooled to liquid nitrogen temperatures.
Paul Matsudaira is Professor and Head of the Department of Biological Science at the National University of Singapore. For more information, please visit: http://www.dbs.nus.edu.sg/staff/paul.html