Dielectrophoretic Control of Particle Assembly in the Presence of Photoresist Posts: Simulation and Experiment

Alternating current (AC) electric fields allow for reconfigurability and tunability of particle assemblies as a result of dielectrophoresis (DEP) in conjunction with van der Waals, gravitational and electrostatic forces. Since these assemblies are reconfigurable, they are of interest for creating tunable metamaterials and endowing other favorable optical properties. To create assemblies for tunable optics, it is important to understand the behavior of optically relevant particle suspensions. Electric field-mediated assemblies have been studied with silicon dioxide (SiO2) and poly (methyl methacrylate) (PMMA) particles, which differ in permittivity, using a quadrupole electrode geometry and in the presence of photoresist posts. COMSOL multiphysics software was used to simulate the electric field gradient for three different post diameters and spacing conditions that correspond to experimental samples. The resulting information was used later for Monte Carlo simulations to study the behavior of both types of particles in presence of DEP, van der Waals, electrostatic, and gravitational forces, as well as verifying the experimental results when changing parameters such as post diameters and distances, particle materials and concentration, and voltages. We observe a variety of different assemblies, in which the particles are wither attracted to or repelled from the posts – consistent with experiment. These simulations indicate that optimal conditions can be defined for a material with given optical properties.