FIELD-INDUCED LAYERING OF COLLOIDAL CRYSTALS

An electrohydrodynamic methodology has been developed that makes possi ble the precise assembly of two- and three-dimensional colloidal cryst als on electrode surfaces. Electrophoretically deposited colloidal par ticles were observed to move toward one another over very large distan ces (greater than five particle diameters) to form two-dimensional col loidal crystals for both micrometer- and nanometer-size particles, Thi s coalescence of particles with the same charge is opposite to what is expected from electrostatic considerations and appears to result from electrohydrodynamic fluid flow arising from an ionic current flowing through the solution. The ability to modulate this ''lateral attractio n'' between particles, by adjusting field strength or frequency, facil itates the reversible formation of two-dimensional fluid and crystalli ne colloidal states on the electrode surface. Further manipulation all ows controlled structures to be assembled.