  The interplay between shape anisotropy and directed long-range interactions
enables the self-assembly of complex colloidal structures. As a recent
highlight, ellipsoidal particles polarized in an external electric field were
observed to associate into well-defined tubular structures. In this study, we
investigate systematically such directed self-assembly using Monte Carlo
simulations of a two-point-charge model of polarizable prolate ellipsoids. In
spite of its simplicity and computational efficiency, we demonstrate that the
model is capable of capturing the complex structures observed in experiments on
ellipsoidal colloids at low volume fractions. We show that, at sufficiently
high electric field strength, the anisotropy in shape and electrostatic
interactions causes a transition from 3-dimensional crystal structures observed
at low aspect ratios to 2-dimensional sheets and tubes at higher aspect ratios.
Our work thus illustrates the rich self-assembly behavior accessible when
exploiting the interplay between competing long- and short-range anisotropic
interactions in colloidal systems.
