(409b) Controlling Anisotropic Colloidal Assembly in External Fields

The ability to assemble anisotropic nano- and micro- colloidal particles into hierarchically ordered structures that are also potentially reconfigurable provides the basis for exotic materials (e.g. photonic, negative refraction) and controllable devices in emerging technologies (e.g. optical computing, sub-diffraction limit imaging, invisibility cloaking). However, current capabilities to produce such ordered materials with a sufficiently low defect density have limited the development of the science and applications of such materials. These limitations are due to fundamental problems with designing, controlling, and optimizing the thermodynamics and kinetics of assembly processes for complex colloidal components. As a result, there is an interest in understanding how thermal motion, particle interactions, patterned surfaces, and external fields can be optimally coupled to robustly control the assembly of colloidal components into hierarchically structured functional meta-materials.

Our approach to this problem is to use inhomogeneous AC electric fields to manipulate the position, orientation, and assembly of tri-axial super-ellipsoidal colloids. We begin by first developing rigorous potentials to capture the position and orientation dependent DLVO particle-substrate and particle-particle, dipole-field and dipole-dipole interactions. Microscopy results are used to validate these theoretical expressions by showing measured and modeled potential energy landscapes for up to twelve unique states for single tri-axial particles (including all combinations of position and orientation). We then show how assemblies of many particles can be used to obtain a variety of equilibrium microstructures of super-ellipsoidal colloids. Finally, with the ability to measure, model, and tune anisotropic colloidal interactions and dynamics in inhomogeneous electric fields, we demonstrate how time-varying fields can be used to manipulate non-equilibrium pathways for the assembly, disassembly, reconfiguration, and repair of hierarchically ordered anisotropic colloidal microstructures.