29 research outputs found
Defect configurations and dynamical behavior in a Gay-Berne nematic emulsion
To model a nematic emulsion consisting of a surfactant-coated water droplet
dispersed in a nematic host, we performed a molecular dynamics simulation of a
droplet immersed in a system of 2048 Gay-Berne ellipsoids in a nematic phase.
Strong radial anchoring at the surface of the droplet induced a Saturn ring
defect configuration, consistent with theoretical predictions for very small
droplets. A surface ring configuration was observed for lower radial anchoring
strengths, and a pair of point defects was found near the poles of the droplet
for tangential anchoring. We also simulated the falling ball experiment and
measured the drag force anisotropy, in the presence of strong radial anchoring
as well as zero anchoring strength.Comment: 17 pages, 15 figure
Simulating Particle Dispersions in Nematic Liquid-Crystal Solvents
A new method is presented for mesoscopic simulations of particle dispersions
in nematic liquid crystal solvents. It allows efficient first-principle
simulations of the dispersions involving many particles with many-body
interactions mediated by the solvents. A simple demonstration is shown for the
aggregation process of a two dimentional dispersion.Comment: 5 pages, 5 figure
Friction Drag on a Particle Moving in a Nematic Liquid Crystal
The flow of a liquid crystal around a particle does not only depend on its
shape and the viscosity coefficients but also on the direction of the
molecules. We studied the resulting drag force on a sphere moving in a nematic
liquid crystal (MBBA) in a low Reynold's number approach for a fixed director
field (low Ericksen number regime) using the computational artificial
compressibility method. Taking the necessary disclination loop around the
sphere into account, the value of the drag force anisotropy
(F_\perp/F_\parallel=1.50) for an exactly computed field is in good agreement
with experiments (~1.5) done by conductivity diffusion measurements. We also
present data for weak anchoring of the molecules on the particle surface and of
trial fields, which show to be sufficiently good for most applications.
Furthermore, the behaviour of the friction close to the transition point
nematic isotropic and for a rod-like and a disc-like liquid crystal will be
given.Comment: 23 pages RevTeX, including 3 PS figures, 1 PS table and 1 PS-LaTeX
figure; Accepted for publication in Phys. Rev.
A Smooth Interface Method for Simulating Liquid Crystal Colloid Dispersions
A new method is presented for mesoscopic simulations of particle dispersions
in liquid crystal solvents. It allows efficient first-principle simulations of
the dispersions involving many particles with many-body interactions mediated
by the solvents. Demonstrations have been performed for the aggregation of
colloid dispersions in two-dimensional nematic and smectic-C* solvents
neglecting hydrodynamic effects, which will be taken into account in the near
future.Comment: 13 pages, 4 figure
Effective interactions of colloids on nematic films
The elastic and capillary interactions between a pair of colloidal particles
trapped on top of a nematic film are studied theoretically for large
separations . The elastic interaction is repulsive and of quadrupolar type,
varying as . For macroscopically thick films, the capillary interaction
is likewise repulsive and proportional to as a consequence of
mechanical isolation of the system comprised of the colloids and the interface.
A finite film thickness introduces a nonvanishing force on the system (exerted
by the substrate supporting the film) leading to logarithmically varying
capillary attractions. However, their strength turns out to be too small to be
of importance for the recently observed pattern formation of colloidal droplets
on nematic films.Comment: 13 pages, accepted by EPJ
Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host
Combining molecular dynamics and Monte Carlo simulation we study defect
structures around an elongated colloidal particle embedded in a nematic liquid
crystal host. By studying nematic ordering near the particle and the
disclination core region we are able to examine the defect core structure and
the difference between two simulation techniques. In addition, we also study
the torque on a particle tilted with respect to the director, and modification
of this torque when the particle is close to the cell wall
Topological Defects and Interactions in Nematic Emulsions
Inverse nematic emulsions in which surfactant-coated water droplets are
dispersed in a nematic host fluid have distinctive properties that set them
apart from dispersions of two isotropic fluids or of nematic droplets in an
isotropic fluid. We present a comprehensive theoretical study of the
distortions produced in the nematic host by the dispersed droplets and of
solvent mediated dipolar interactions between droplets that lead to their
experimentally observed chaining. A single droplet in a nematic host acts like
a macroscopic hedgehog defect. Global boundary conditions force the nucleation
of compensating topological defects in the nematic host. Using variational
techniques, we show that in the lowest energy configuration, a single water
droplet draws a single hedgehog out of the nematic host to form a tightly bound
dipole. Configurations in which the water droplet is encircled by a
disclination ring have higher energy. The droplet-dipole induces distortions in
the nematic host that lead to an effective dipole-dipole interaction between
droplets and hence to chaining.Comment: 17 double column pages prepared by RevTex, 15 eps figures included in
text, 2 gif figures for Fig. 1