Chunfeng Zhou, Pengtao Yue & James J. Feng
Langmuir 24, 3099-3110 (2008)
Abstract - We use dynamic simulations to
explore the pairwise interaction and multi-particle assembly of
droplets suspended in a nematic liquid crystal. The computation is
based on a regularized Leslie-Ericksen theory that allows orientational
defects. The homeotropic anchoring on the drop surface is of sufficient
strength as to produce a satellite point defect near the droplet. Based
on the position of the defects relative to the host droplet and the
far-field molecular orientation, we have identified five types of
pairwise attractive and repulsive forces. In particular, long-range
attraction between two droplets with their line of centers along the
far-field orientation decays as R-4
with the center-to-center separation R. This agrees with prior
static calculations and a phenomenological model that treats the
attraction as that between two dipoles. For interaction in shorter
ranges, our simulations agree qualitatively with experimental
measurements and static calculations. However, there is considerable
quantitative discrepancy among the few existing studies and our
simulation. We suggest that this is partly due to the dynamic nature of
the process, which has never been taken into account in prior
calculations. Multi-drop simulations show the formation of linear
chains through pairwise interactions between nearby droplets. Parallel
chains repel or attract each other depending on the relative
orientation of the drop-to-defect vector. These are consistent with
experimental observations of chain formation and two-dimensional
self-assembly in bulk nematics and smectic-C films.