1,169 research outputs found
External and intrinsic anchoring in nematic liquid crystals: A Monte Carlo study
We present a Monte Carlo study of external surface anchoring in nematic cells
with partially disordered solid substrates, as well as of intrinsic anchoring
at free nematic interfaces. The simulations are based on the simple hexagonal
lattice model with a spatially anisotropic intermolecular potential. We
estimate the corresponding extrapolation length by imposing an elastic
deformation in a hybrid cell-like nematic sample. Our estimates for
increase with increasing surface disorder and are essentially
temperature--independent. Experimental values of are approached only when
both the coupling of nematic molecules with the substrate and the anisotropy of
nematic--nematic interactions are weak.Comment: Revisions primarily in section I
Imbibition in mesoporous silica: rheological concepts and experiments on water and a liquid crystal
We present, along with some fundamental concepts regarding imbibition of
liquids in porous hosts, an experimental, gravimetric study on the
capillarity-driven invasion dynamics of water and of the rod-like liquid
crystal octyloxycyanobiphenyl (8OCB) in networks of pores a few nanometers
across in monolithic silica glass (Vycor). We observe, in agreement with
theoretical predictions, square root of time invasion dynamics and a sticky
velocity boundary condition for both liquids investigated.
Temperature-dependent spontaneous imbibition experiments on 8OCB reveal the
existence of a paranematic phase due to the molecular alignment induced by the
pore walls even at temperatures well beyond the clearing point. The ever
present velocity gradient in the pores is likely to further enhance this
ordering phenomenon and prevent any layering in molecular stacks, eventually
resulting in a suppression of the smectic phase in favor of the nematic phase.Comment: 18 pages, 8 figure
Some properties of membranes in nematic solvents
The fluctuation spectrum of membranes in nematic solvents is altered by the
boundary condition imposed on the bulk nematic director by the curved membrane.
We discuss some properties of single and multi-membrane systems in nematic
solvents, primarily based on the Berreman-de~Gennes model. We show that:
membranes in nematic solvents are more rigid and less rough than in their
isotropic counterparts; have a different Helfrich steric stabilization energy,
proportional to , and hence a different compression modulus in the
lamellar state; and can exhibit phase separation via unbinding during a quench
into the nematic state. We also discuss the preparation and possible
experimental effects of nematic-mediated surfactant membrane system
Colloidal Particles at Chiral Liquid Crystal Interfaces
Colloidal particles trapped at an interface between two fluids can form a
wide range of different structures. Replacing one of the fluid with a liquid
crystal increases the complexity of interactions and results in a greater range
of possible structures. New behaviour emerges when colloidal particles interact
with defects in the liquid crystal phases. Here we discuss the templating of
colloids at a cholesteric isotropic interface.Comment: 7 pages, 5 figure
Visualization of boundary-layer development on turbomachine blades with liquid crystals
This report documents a study of the use of liquid crystals to visualize boundary layer development on a turbomachine blade. A turbine blade model in a linear cascade of blades was used for the tests involved. Details of the boundary layer development on the suction surface of the turbine blade model were known from previous research. Temperature sensitive and shear sensitive liquid crystals were tried as visual agents. The temperature sensitive crystals were very effective in their ability to display the location of boundary layer flow separation and reattachment. Visualization of natural transition from laminar to turbulent boundary layer flow with the temperature sensitive crystals was possible but subtle. The visualization of separated flow reattachment with the shear sensitive crystals was easily accomplished when the crystals were allowed to make a transition from the focal-conic to a Grandjean texture. Visualization of flow reattachment based on the selective reflection properties of shear sensitive crystals was achieved only marginally because of the larger surface shear stress and shear stress gradient levels required for more dramatic color differences
Nematic - Isotropic Transition in Porous Media - a Monte Carlo Study
We propose a lattice model to simulate the influence of porous medium on the
Nematic - Isotropic transition of liquid crystal confined to the pores. The
effects of pore size and pore connectivity are modelled through a disorder
parameter. Monte Carlo calculations based on the model leads to results that
compare well with experiments.Comment: 11 pages; 4 figure
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