65 research outputs found
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.
Drag on particles in a nematic suspension by a moving nematic-isotropic interface
We report the first clear demonstration of drag on colloidal particles by a moving nematic-isotropic
interface. The balance of forces explains our observation of periodic, strip-like structures that are produced by the movement of these particles
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
Dynamics of gravity driven three-dimensional thin films on hydrophilic-hydrophobic patterned substrates
We investigate numerically the dynamics of unstable gravity driven
three-dimensional thin liquid films on hydrophilic-hydrophobic patterned
substrates of longitudinal stripes and checkerboard arrangements. The thin film
can be guided preferentially on hydrophilic longitudinal stripes, while fingers
develop on adjacent hydrophobic stripes if their width is large enough. On
checkerboard patterns, the film fingering occurs on hydrophobic domains, while
lateral spreading is favoured on hydrophilic domains, providing a mechanism to
tune the growth rate of the film. By means of kinematical arguments, we
quantitatively predict the growth rate of the contact line on checkerboard
arrangements, providing a first step towards potential techniques that control
thin film growth in experimental setups.Comment: 30 pages, 12 figure
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
Capillary filling with wall corrugations] Capillary filling in microchannels with wall corrugations: A comparative study of the Concus-Finn criterion by continuum, kinetic and atomistic approaches
We study the impact of wall corrugations in microchannels on the process of
capillary filling by means of three broadly used methods - Computational Fluid
Dynamics (CFD), Lattice-Boltzmann Equations (LBE) and Molecular Dynamics (MD).
The numerical results of these approaches are compared and tested against the
Concus-Finn (CF) criterion, which predicts pinning of the contact line at
rectangular ridges perpendicular to flow for contact angles theta > 45. While
for theta = 30, theta = 40 (no flow) and theta = 60 (flow) all methods are
found to produce data consistent with the CF criterion, at theta = 50 the
numerical experiments provide different results. Whilst pinning of the liquid
front is observed both in the LB and CFD simulations, MD simulations show that
molecular fluctuations allow front propagation even above the critical value
predicted by the deterministic CF criterion, thereby introducing a sensitivity
to the obstacle heigth.Comment: 25 pages, 8 figures, Langmuir in pres
Halloween and the feast of Ivan Kupala: similarities and differences
The Youth of the 21st Century: Education, Science, Innovations : Proceedings of VI International Conference for Students, Postgraduates and Young Scientists, Vitebsk, December 12, 2019. - Vitebsk : Vitebsk State University named after P. M. Masherov, 2019. - P. 76-78. - Bibliogr.: p. 77-78 (5 nam.)
Creating localized mixing stations within microfluidic channels.
Simulations show how the flow and phase behavior of binary fluids in microchannels can be regulated by introducing solvophilic and solvophobic patches onto the underlying substrate. Depending on the arrangement of these patches, the two fluids can be driven to "switch" positions or undergo extensive mixing within a specific region of the channel. The results open the possibility for creating spatially controlled reaction chambers within microfluidic devices
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