(484f) Design of Multipolar Colloidal Rods Using Discontinuous Molecular Dynamics

Authors: 
Rutkowski, D., North Carolina State University
Hall, C. K., North Carolina State University
Velev, O. D., North Carolina State University

Colloids with anisotropic charge distributions hold promise for creating a number of useful new materials including optic materials with novel symmetries, electrical materials for information storage, and dampers for controlling vibrations in structures. Because experimental characterization of the many possible types of multipolar colloidal particles that could form is difficult, the search for novel colloidal materials can be enhanced and guided by simulations of colloidal system assembly. Using a simplified potential, we have simulated a system of dipolar rods with various aspect ratios using discontinuous molecular dynamics (DMD). Each dipolar rod was modeled as several overlapping spheres held in a rod shape to represent excluded volume and two smaller, embedded spheres to represent the charges that make up the extended dipole. We have discovered the existence of fluid, string-fluid, and “gel” phases at low volume fractions and nematic phases at high volume fractions. We have also developed a more realistic discontinuous Yukawa-like potential that allows us to examine colloidal rods that exhibit either head-to-tail or side-by-side configurations depending on the internal charge separation. The percolation probability, maximum cluster size and heat capacity have been monitored to evaluate the aggregation properties of these particles as a function of temperature. The mean squared displacement (MSD) has also been calculated to follow the dynamics. Preliminary results show that at low temperatures the rods assemble to form strands when the head-to-tail configuration is preferred and into rectangular aggregates when the side-by-side configuration is preferred. While the above simulations were all performed in 3d, we have also performed 2d simulations of the same system of dipolar rods corresponding more closely to experiments in which the colloidal particles are confined between plates. Finally, we have also looked into the effect that adding an external electric field has on the system and have observed an increased propensity for chaining in the system.