(525c) Design of Multipolar Colloidal Rods Using Discontinuous Molecular Dynamics
Colloids with anisotropic charge distributions hold promise for creating a number of useful new materials including optical materials with novel symmetries, electrical materials for information storage, and dampers for controlling vibrations in structures. Because the experimental characterization of the many possible types of multipolar colloidal particles is currently infeasible, the search for novel colloidal materials can be enhanced and guided by simulations of colloidal system assembly. We have simulated a system of dipolar rods with an aspect ratio of 2 to 1 using discontinuous molecular dynamics (DMD). Each dipolar rod was modeled as three overlapping spheres held in a rod shape to represent excluded volume and two smaller, embedded spheres to represent the charges that make up the dipole. From NVT simulations of these particles we have discovered the existence of fluid, string-fluid, and “gel” phases at low volume fractions and nematic phases at high volume fractions. A phase diagram has been constructed using a variety of methods to delineate the boundaries between the various phases. Our nematic phase boundary at high volume fraction and temperature is consistent with results from Frenkel and Bolhuis on hard spherocylinders. Additionally, we have found evidence for temperature-dependent hexagonal and square ordering for the rods at high volume fractions. We have also simulated dipolar rods of various lengths to learn how this modifies the phase diagram.