AXIAL ESCAPE OF NEMATICS IN BEND-CYLINDRICAL CONFIGURATION

1993 ◽  
Vol 07 (04) ◽  
pp. 1143-1156 ◽  
Author(s):  
A. SPARAVIGNA ◽  
A. STRIGAZZI ◽  
P. PALFFY-MUHORAY
Keyword(s):  
Liquid Crystal ◽  
Elastic Constant ◽  
Order Parameter ◽  
Critical Thickness ◽  
External Surface ◽  
First Order ◽  
Concentric Cylinders ◽  
Anchoring Strength ◽  
Strong Anchoring

We investigated the possibility of axial escape of a nematic liquid crystal confined between two concentric cylinders with surface-imposed pure bend distortion. We found that this effect appears also in the case of strong anchoring. When the twist-anchoring is weak only at one of the surfaces, the critical thickness dc of the structure is affected by the saddle-splay elastic constant K24. Moreover, if the twist-anchoring is weak at the external surface, a transition of the first order was found, dc playing the role of an order parameter. Such a transition, characterized by bistability and hysteresis, may be driven by K24 and by the anchoring strength.

SOME CONSIDERATIONS ON THE INFLUENCE OF THE FLEXOELECTRICITY ON THE CRITICAL THICKNESS OF A HYBRID ALIGNED NEMATIC CELL

1993 ◽  
Vol 07 (04) ◽  
pp. 1131-1141 ◽  
Author(s):  
A.L. ALEXE-IONESCU
Keyword(s):  
Liquid Crystal ◽  
Elastic Constant ◽  
Nematic Liquid Crystal ◽  
Critical Thickness ◽  
Liquid Crystal Cell ◽  
Steric Interaction ◽  
Dispersion Forces ◽  
Elastic Coefficient ◽  
Energy Dispersion ◽  
Anchoring Energy

We discuss the influence of flexoelectricity on the critical thickness of a hybrid aligned nematic liquid crystal cell, taking into account the surface-like volume elasticity and supposing that the anchoring energy is due only to the dispersion forces. We show that the critical thickness is independent of the flexoelectrical properties of the nematic liquid crystal, and that this conclusion is valid also in the case of generic anchoring energy (dispersion+steric interaction). Furthermore, the possibility of spontaneous Freedericksz transition is shown according to the importance of the elastic coefficient associated to the surface-like volume elasticity with respect to the splay elastic constant.

A statistical theory of liquid crystalline mixtures: phase separation

1976 ◽  
Vol 352 (1668) ◽  
pp. 41-56 ◽  
Keyword(s):  
Liquid Crystal ◽  
Phase Separation ◽  
Liquid Crystalline ◽  
Experimental Studies ◽  
Phase Region ◽  
Crystal Formation ◽  
Two Phase ◽  
First Order ◽  
Repulsive Forces

The molecular field theory of multicomponent liquid crystalline mixtures, developed by Humphries, James & Luckhurst, has been extended to investigate the possibility of phase separation in binary mixtures of rods and spheres. This extension indicates that the addition of a spherical solute to a liquid crystal depresses the transition from the isotropic to the nematic phase. The solute induced phase transition is first order, although the nematic and isotropic phases are found to be separated by a two-phase region consisting of both nematic and isotropic phases. These qualitative conclusions of the theory are in complete accord with experiment and there is also reasonable agreement with certain quantitative predictions. The same problem has been tackled using a lattice model with purely repulsive anisotropic interactions; this theory would appear to be marginally less successful than our own which is based on a weaker anisotropic potential. Consequently it is not possible to use experimental studies of phase separation in binary liquid crystal mixtures to demonstrate the rôle of repulsive forces in liquid crystal formation.

scholarly journals Expulsion of disclinations in nematic liquid crystals

2003 ◽  
Vol 14 (1) ◽  
pp. 39-59 ◽  
Author(s):  
PAOLO BISCARI ◽  
TIMOTHY J. SLUCKIN
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Boundary Conditions ◽  
Half Space ◽  
Nematic Liquid Crystal ◽  
Nematic Liquid Crystals ◽  
Critical Value ◽  
Repulsive Force ◽  
Anchoring Strength ◽  
Strong Anchoring

We study the interactions between a nematic liquid crystal disclination and the surface of the half-space which bounds it. When strong anchoring conditions are applied on the boundary, the biaxial core of the disclination affects the repulsive force that tends to drive the disclination away from the surface. If we replace the strong boundary conditions with an anchoring potential, the surface-disclination interaction depends on the surface extrapolation length. In particular, the nematic may expel the disclination if the anchoring strength is below a critical value.

Freedericksz transition in Ferronematic Liquid Crystal under weak anchoring conditions

2021 ◽  
Author(s):  
T. Lahiri ◽  
S. K. Pushkar ◽  
P. Poddar
Keyword(s):  
Liquid Crystal ◽  
Landau Theory ◽  
Colloidal Suspension ◽  
Present Theory ◽  
Threshold Field ◽  
Ferromagnetic Nanoparticles ◽  
First Order ◽  
Segregation Effect ◽  
Experimental Findings ◽  
Strong Anchoring

Abstract Freedericksz effect is investigated theoretically for a ferronematic liquid crystal, which is a colloidal suspension of ferromagnetic nanoparticles in a nematic fluid. Considering a splay type Freedericksz geometry, weak anchoring conditions are assumed at the cell boundaries. The specific nature of this anchoring reveals a rich variety of stable ferronematic phases, which include uniform, distorted and saturated states. Apart from weak anchoring conditions at the cell boundaries, soft planar anchoring is assumed for the mesogenic molecules at the surface of a nanoparticle. The interplay between these two anchoring phenomena along with Frank type elastic theory determine the values of Freedericksz threshold between various ferronematic states. It is found that compared to relatively strong anchoring for the mesogens both at the cell boundaries and at the surface of the nanoparticles, weak anchoring significantly reduces the Freedericksz threshold field. Landau theory is then utilized to understand the nature of transition between different ferronematic states. Based on the phenomenon of segregation effect, these transitions are found to be either first order or second order in nature. The present theory is also extended to non-ferromagnetic nanoparticles and significant reduction in Freedericksz threshold is obtained. Finally, these results are corroborated with experimental findings.

Exploring Baryon Rich Matter with Heavy-Ion Collisions

2019 ◽  
Vol 64 (7) ◽  
pp. 583 ◽  
Author(s):  
S. Harabasz
Keyword(s):  
Center Of Mass ◽  
Heavy Ion ◽  
State Density ◽  
Heavy Nuclei ◽  
First Order ◽  
Center Of Mass Energy ◽  
Ion Collisions ◽  
Deconfinement Phase Transition ◽  
Ground State Density

Collisions of heavy nuclei at (ultra-)relativistic energies provide a fascinating opportunity to re-create various forms of matter in the laboratory. For a short extent of time (10-22 s), matter under extreme conditions of temperature and density can exist. In dedicated experiments, one explores the microscopic structure of strongly interacting matter and its phase diagram. In heavy-ion reactions at SIS18 collision energies, matter is substantially compressed (2–3 times ground-state density), while moderate temperatures are reached (T < 70 MeV). The conditions closely resemble those that prevail, e.g., in neutron star mergers. Matter under such conditions is currently being studied at the High Acceptance DiElecton Spectrometer (HADES). Important topics of the research program are the mechanisms of strangeness production, the emissivity of matter, and the role of baryonic resonances herein. In this contribution, we will focus on the important experimental results obtained by HADES in Au+Au collisions at 2.4 GeV center-of-mass energy. We will also present perspectives for future experiments with HADES and CBM at SIS100, where higher beam energies and intensities will allow for the studies of the first-order deconfinement phase transition and its critical endpoint.

scholarly journals Azimuthal Anchoring Strength in Photopatterned Alignment of a Nematic

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 675
Author(s):  
H. Nilanthi Padmini ◽  
Mojtaba Rajabi ◽  
Sergij V. Shiyanovskii ◽  
Oleg D. Lavrentovich
Keyword(s):  
Liquid Crystal ◽  
Point Defects ◽  
Elastic Energy ◽  
Separation Distance ◽  
Thin Layers ◽  
Uv Exposure ◽  
Surface Anchoring ◽  
Anchoring Strength ◽  
Spatially Varying

Spatially-varying director fields have become an important part of research and development in liquid crystals. Characterization of the anchoring strength associated with a spatially-varying director is difficult, since the methods developed for a uniform alignment are seldom applicable. Here we characterize the strength of azimuthal surface anchoring produced by the photoalignment technique based on plasmonic metamsaks. The measurements used photopatterned arrays of topological point defects of strength +1 and −1 in thin layers of a nematic liquid crystal. The integer-strength defects split into pairs of half-integer defects with lower elastic energy. The separation distance between the split pair is limited by the azimuthal surface anchoring, which allows one to determine the strength of the latter. The strength of the azimuthal anchoring is proportional to the UV exposure time during the photoalignment of the azobenzene layer.

Polar Anchoring Strength and the Temperature Dependence of Nematic Liquid Crystal (5CB) Aligned on Rubbed Polystyrene Films

1992 ◽  
Vol 31 (Part 1, No. 7) ◽  
pp. 2165-2169 ◽  
Author(s):  
Dae-Shik Seo ◽  
Koh-ichi Muroi ◽  
Toh-ru Isogami ◽  
Hideaki Matsuda ◽  
Shunsuke Kobayashi
Keyword(s):  
Liquid Crystal ◽  
Temperature Dependence ◽  
Nematic Liquid Crystal ◽  
Anchoring Strength ◽  
Liquid Crystal 5Cb

scholarly journals Liquid Crystal Ordering in the Hexagonal Phase of Rod-Coil Diblock Copolymers

Polymers ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1262
Author(s):  
Mikhail A. Osipov ◽  
Maxim V. Gorkunov ◽  
Alexander A. Antonov
Keyword(s):  
Liquid Crystal ◽  
Order Parameter ◽  
Density Functional ◽  
Diblock Copolymers ◽  
Microphase Separation ◽  
Hexagonal Phase ◽  
Orientational Order ◽  
Order Parameters ◽  
Copolymer Composition ◽  
Rigid Rod

Density functional theory of rod-coil diblock copolymers, developed recently by the authors, has been generalised and used to study the liquid crystal ordering and microphase separation effects in the hexagonal, lamellar and nematic phases. The translational order parameters of rod and coil monomers and the orientational order parameters of rod-like fragments of the copolymer chains have been determined numerically by direct minimization of the free energy. The phase diagram has been derived containing the isotropic, the lamellar and the hexagonal phases which is consistent with typical experimental data. The order parameter profiles as functions of temperature and the copolymer composition have also been determined in different anisotropic phases. Finally, the spatial distributions of the density of rigid rod fragments and of the corresponding orientational order parameter in the hexagonal phase have been calculated.

scholarly journals Triggering avalanches by transverse perturbations in a rotating drum

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Vicente Salinas ◽  
Cristóbal Quiñinao ◽  
Sebastián González ◽  
Gustavo Castillo
Keyword(s):  
Hopf Bifurcation ◽  
Theoretical Model ◽  
Order Parameter ◽  
Small Scale ◽  
Rotating Drum ◽  
Governing Parameter ◽  
Stick Slip ◽  
Slip Regime ◽  
Axis Of Rotation

AbstractWe study the role of small-scale perturbations in the onset of avalanches in a rotating drum in the stick-slip regime. By vibrating the system along the axis of rotation with an amplitude orders of magnitude smaller than the particles’ diameter, we found that the order parameter that properly describes the system is the kinetic energy. We also show that, for high enough frequencies, the onset of the avalanche is determined by the amplitude of the oscillation, contrary to previous studies that showed that either acceleration or velocity was the governing parameter. Finally, we present a theoretical model that explains the transition between the continuous and discrete avalanche regimes as a supercritical Hopf bifurcation.

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