(527b) Manipulation And Assembly Of Colloidal Particles Into Quasicrystals Via Dielectrophoresis

Self-assembly lies at the heart of creating functional nanomaterials and has relevance to technological applications ranging from catalysis to cosmetics. Traditional methods of synthesizing nanomaterials with precision control of particle size, pore size, and functionality rely on complex synthesis routes and are usually impractical for scale-up production of functional nanomaterials. Recently, there is the emerging interest in using dielectrophoresis (DEP) to assemble colloidal particles into desirable packing configuration. With traditional methods of electrophoretic assembly, very high electrical power has to be applied in order to facilitate colloidal assembly. In this work, we incorporate microelectrodes into microfluidic devices to allow us to manipulate and assemble polydisperse colloidal particles into quasi-crystals at low amplitudes. Our results show a strong dependence of the DEP mobility towards the high and low field regions on the interparticle interaction and consequently the final structure of colloidal aggregates. A cross-over from positive DEP to negative DEP beyond a cross-over frequency has been observed for the latex and silica aqueous suspensions in our work. Using a ternary system of colloidal silica particles of varying diameters, we are able to tailor 3-D structures and monitor the assembly process via high-speed confocal microscopy. When the applied frequency is below or above the crossover frequencies of silica particles of difference sizes, particles repel each other and no aggregation is observed. Within a narrow range between two cross-over frequencies, we are able to form quasi-crystals by controlling particle segregation. We also present a mechanism for the assembly process and the formation of quasicrystalline structures.