(59a) Structure of Spherical Silica Colloid Film Prepared By Electrophoretic Deposition in Pulsed Direct Current Electric Field

Colloidal crystal is of an ordered structure comprising regularly arrayed (in 2D) or deposited (in 3D) spherical colloidal particles. Owing to its unique optical properties resulting from Bragg reflection, it is expected to have it applied to optical devices, such as tunable laser and color materials not suffering from color fade-out. Several methods have been proposed and attempted to fabricate 3D colloidal crystals, including the dip coating method, the sedimentation method, and the convective self-assembly method. The 3D colloidal crystal fabrication, however, requires precise operations as well as prolonged time. Electrophoretic deposition is the phenomenon that can attain migration and deposition of colloidal particles toward the electrode upon application of an electric field; it is possible to fabricate a thin film of particles on the electrode with relative ease in comparatively short time. Furthermore, there is additional possibility of controlling the structure of particle thin film because it involves many adjustable operation parameters.

In this study we tried to assemble a 3D ordered structure of particle thin film with spherical silica colloid in ethanol, and found that the hexagonal close-packed structure could be realized by applying a pulsed direct current electric field with 5 to 50 Hz frequency. Based on the calculation results, it is revealed that the deposited particles led to essentially one-particle layer during ON time of the pulsed field and were relaxed through Brownian motion during OFF time of the pulsed field over the given frequency range. It is suggested then that the hcp structure was formed by deposition and re-deposition behavior caused by the pulsed direct current electric field.