We have recently developed a novel and general means of ordering colloidal particles into three-dimensional crystals rapidly and reversibly using electric fields. The ordering mechanism appears to rely on a combination of induced dipole interactions and hydrodynamic flows that push particles together, creating an effective attraction. Because these interactions can be moderated with a combination of applied field properties and confining geometry, their magnitude can be greatly tuned and used to crystallize particles in a wide variety of size ranges. Our preliminary investigations have focused on colloids ranging in size from 250 nm down to 50 nm in radius, all of which can be reversibly crystallized through application of the external field. We have also shown that nucleation of these colloidal crystals can be spatially controlled solely through selective application of the electric field. The goal of the work proposed here is to extend these preliminary investigations into smaller length scales throughout the nanoscale range. We intend to take advantage of this for the reversible and spatially addressable crystallization of nanoscale particles. In addition to the creation of a display technology with inexpensive materials, we envision the development of switchable photonic band gap materials based upon the reversible ordering of nanocolloidal-sized materials. The award has been funded by the Thermal Transport and Thermal Processing Program and the Particulate and Multiphase Processes Program of the Chemical and Transport Systems Division.
