Electric Field-Assisted Convective Assembly of Large-Domain Colloidal Crystals

Jairus Kleinert, Sejong Kim, and Orlin D. Velev. Chemical and Biomolecular Engineering, North Carolina State University, Campus Box 7905, Raleigh, NC 27695-7905

Two-dimensional colloidal crystals are difficult to assemble rapidly and without defects. Convective assembly is an easily implemented and controlled technique for depositing colloidal crystals by evaporation of a microparticle suspension from a withdrawing meniscus, but this method is slow and does not produce large crystal domains. Alternatively, dielectrophoresis has been used to produce large single-orientation crystals rapidly but offers no simple way to immobilize the crystals. We report a new method of convective assembly combined with an AC electric field to increase the long-range order and deposition rate of latex microsphere crystals. With the electric field, electrowetting on dielectric allowed control of the shape of the meniscus and flow on the microscale. Film spreading at the meniscus caused by electrowetting increased the evaporation rate and allowed for more rapid crystal deposition. Another effect of the electric field was dipolar chaining and organization of particles into large single-orientation crystal domains. We have achieved up to a five-fold increase in the rate of crystal deposition and an order of magnitude increase in crystal domain size compared to convective assembly without an electric field. This work provides a basis for establishing an improved large-scale colloidal crystal assembly process.