Switchable dielectrophoresis of defect-free droplets in an anisotropic liquid crystal medium

Quantum Dot Arrays Fabricated Using In Situ Photopolymerization of a Reactive Mesogen and Dielectrophoresis

Dielectrophoresis (DEP) is an excellent tool for manipulating small particles within a liquid or gas medium. However, when the size of the particles is too small, such as with quantum dots (QDs), it is difficult to manipulate the particles using DEP because the dielectrophoretic force (F_DEP) depends on the volume of the particles and is therefore too weak to achieve particle migration. Herein, we demonstrate a novel method for controlling nanoscale QD particles using DEP by introducing photopolymerized reactive mesogen (RM) bead vehicles. The size of an RM bead is well-controlled by the RM concentration in the medium, and when the size is approximately 0.2 μm or larger, the RM beads can be arbitrarily manipulated using DEP under moderate electric fields. Interestingly, during photopolymerization, QD particles are easily absorbed by polymerized RM beads and most of the QDs are embedded within the RM beads. Hence, we can fabricate periodic QD arrays by manipulating the RM beads containing such dots. In addition, we can fabricate multicolor QD arrays by repeating the processes using different QD particles. The shape of a DEP-assisted QD-RM network pattern can be precisely predicted by calculating the gradient of the square of the electric field (∇E²) and the corresponding F_DEP. This new technology may be useful for the fabrication of optical devices, displays, photonic crystal devices, and bioapplications.

Generation and manipulation of isotropic droplets in nematic medium using switchable dielectrophoresis

Dielectrophoresis (DEP) in a medium with anisotropic dielectric susceptibility is very different from typical DEP in an isotropic medium: The direction of particle actuation can be switched depending on the direction of the susceptibility tensor of the medium. However, the understanding of switchable DEP (SDEP) in an anisotropic medium is still in its infant stage. Here, we investigate SDEP using heat-generated isotropic droplets in a nematic liquid crystal (LC) medium. We demonstrate that the location of the generation of isotropic droplets can be partially controlled by controlling the temperature gradient within the LC cell using dielectric loss. The SDEP actuation of isotropic droplets is also highly dependent on the location of the isotropic droplets. Using this method, we fabricated different array patterns of isotropic and nematic phase separations under different applied signals.