Many-body Effects in Anisotropic Dielectric Colloids: Polarization, Electrostatic Interactions, and Van der Waals Forces

Abstract

We study the polarizability of colloidal particles, as well as their interparticle interactions in the presence or absence of an external electric field. To this end, we employ the Coupled Dipole Method (CDM), which models the particles as clusters of Lorentz atoms (i.e., inducible dipoles) and uses a Hamiltonian approach and large-matrix manipulation to account for all many-atom effects. In this way, we are able to numerically and, in some cases, analytically calculate London-Van der Waals forces, polarizability, orientational energy in an external electric field, and external electric field-induced interparticle interactions. We investigate the polarizability of cuboids, bowls and dumbbells and study their alignment properties in an external electric field. We also investigate the effect of the size and shape of the particles on their tendency to align. For spheres and cubes in an external electric field we study the local polarization in detail and compare the results from the CDM with those from continuum electrostatics to investigate the equivalence of the two approaches. We also study the pair interaction between various particles in an external electric field, taking into account the influence the particles have on each other's polarization and compare the CDM results with those given by techniques that model the particles as built up from permanent dipoles as opposed to induced ones. Using the CDM, we moreover study the London-Van der Waals interaction between various particle shapes in the absence of an external electric field, and whether many-body effects can account for experimentally observed spontaneous chain formation. Lastly, we study the density of states in a string of Lorentz atoms, the evolution of modes on a pair of squares of Lorentz atoms as a function of the gap between the squares, and the interaction of a rod with a conducting plate under the influence of an external electric field.