9 research outputs found
Maier-Saupe-type theory of ferroelectric nanoparticles in nematic liquid crystals
Several experiments have reported that ferroelectric nanoparticles have
drastic effects on nematic liquid crystals--increasing the isotropic-nematic
transition temperature by about 5 K, and greatly increasing the sensitivity to
applied electric fields. In a recent paper [L. M. Lopatina and J. V. Selinger,
Phys. Rev. Lett. 102, 197802 (2009)], we modeled these effects through a Landau
theory, based on coupled orientational order parameters for the liquid crystal
and the nanoparticles. This model has one important limitation: Like all Landau
theories, it involves an expansion of the free energy in powers of the order
parameters, and hence it overestimates the order parameters that occur in the
low-temperature phase. For that reason, we now develop a new Maier-Saupe-type
model, which explicitly shows the low-temperature saturation of the order
parameters. This model reduces to the Landau theory in the limit of high
temperature or weak coupling, but shows different behavior in the opposite
limit. We compare these calculations with experimental results on ferroelectric
nanoparticles in liquid crystals.Comment: 7 pages, including 2 postscript figures, uses REVTeX 4.
Domain and stripe formation between hexagonal and square ordered fillings of colloidal particles on periodic pinning substrates
Using large scale numerical simulations, we examine the ordering of colloidal particles on square periodic
two-dimensional muffin-tin substrates consisting of a flat surface with localized pinning sites. We show
that when there are four particles per pinning site, the particles adopt a hexagonal ordering, while for
five particles per pinning site, a square ordering appears. For fillings between four and five particles per
pinning site, we identify a rich variety of distinct ordering regimes, including disordered grain
boundaries, crystalline stripe structures, superlattice orderings, and disordered patchy arrangements. We
characterize the different regimes using Voronoi analysis, energy dispersion, and ordering of the
domains. We show that many of the boundary formation features we observe occur for a wide range of
other fillings. Our results demonstrate that grain boundary tailoring can be achieved with muffin-tin
periodic pinning substrates