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1.
JETP Letters - It was found that the effect of the ionic modification of anchoring in liquid-crystal droplets can be implemented in the inverse regime. Droplets of 4-n-pentyl-4′-cyanobiphenyl... 相似文献
2.
O. O. Prishchepa A. V. Shabanov V. Ya. Zyryanov A. M. Parshin V. G. Nazarov 《JETP Letters》2007,84(11):607-612
A numerical method has been developed for calculating the director configuration in ellipsoidal droplets of a nematic liquid crystal with strong tangential anchoring in a uniform magnetic field of an arbitrary orientation. A relation has been obtained for determining the Friedericksz threshold corresponding to the beginning of the reorientation of the central region of a droplet when the field is orthogonal to the biopolar axis. The effect of the breaking of the orthogonal condition on the threshold character of the orientation process is considered. The reorientation of the ensemble of bipolar droplets of the 5CB nematic liquid crystal dispersed in polyvinyl butyral has been studied by the magneto-optical method. Comparative analysis of calculation data and measured values of the threshold field has been performed. 相似文献
3.
The films of a polymer-dispersed nematic liquid crystal doped with an ionic surfactant were studied. The surface-anchoring modification effect caused by the local increase in the concentration of surface-active ions was observed at the polymer-liquid crystal interface under the action of an electric field. The modification of the boundary conditions leads to the transformation of the orientational structure of the nematic droplets and, as a result, to an appreciable change in their texture patterns and light-scattering efficiency at the interfaces. The monopolar director configurations (normal and curved) arising in the process of orientational structure transformations are considered and their typical textures are demonstrated. The possibility that the monopolar structure can be formed is theoretically substantiated by the computer simulation of the director field in a nematic droplet with the boundary conditions corresponding to the experiment. 相似文献
4.
We have measured the angular dependence of the surface torque associated with a relatively weak anchoring of a nematic liquid crystal, for large deviations θ (near π/2) from the orientation of minimum energy. Analysing the torque in a Fourier series, we find that in addition to the usual first term, viz. sin 2θ, an important contribution from a sin 6θ term is needed to adequately represent the experimental variation. 相似文献
5.
G. Barbero L.R. Evangelista N.V Madhusudana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):327-331
We analyse the influence of adsorbed ions and the resulting surface electric field and its gradient on the anchoring properties
of nematics with ionic conductivity. We take into account two physical mechanisms for the coupling of the nematic director
with the surface electric field: (i) the dielectric anisotropy and (ii) the coupling of the quadrupolar component of the flexoelectric
coefficient with the field gradient. It is shown that for sufficiently large fields near saturated coverage of the adsorbed
ions, there can be a spontaneous curvature distortion in the cell even when the anchoring energy is infinitely strong. We
also discuss the director distortion when the anchoring energy of the surface is finite.
Received: 29 September 1997 / Received in final from: 10 November 1997 / Accepted: 18 November 1997 相似文献
6.
Influences of surface and flexoelectric polarization on the effective anchoring energy in nematic liquid crystal 下载免费PDF全文
《中国物理 B》2015,(10)
The physical effects on surface and flexoelectric polarization in a weak anchoring nematic liquid crystal cell are investigated systematically. We derive the analytic expressions of two effective anchoring energies for lower and upper substrates respectively as well as their effective anchoring strengths and corresponding tilt angles of effective easy direction.All of these quantities are relevant to the magnitudes of both two polarizations and the applied voltage U. Based on these expressions, the variations of effective anchoring strength and the tilt angle with the applied voltage are calculated for the fixed values of two polarizations. For an original weak anchoring hybrid aligned nematic cell, it may be equivalent to a planar cell for a small value of U and has a threshold voltage. The variation of reduced threshold voltage with reduced surface polarization strength is also calculated. The role of surface polarization is important without the adsorptive ions considered. 相似文献
7.
Deformations of homeotropically aligned flexoelectric nematic layers induced by dc electric fields were simulated numerically. Two different anchoring strengths on the limiting surfaces were assumed. Nematic material was characterised by negative dielectric anisotropy. Both signs of the sum of flexoelectric coefficients were taken into account. The electric properties of the layer were described in terms of a weak electrolyte model. Mobility of cations was assumed to be one order of magnitude lower than that of anions. Quasi-blocking electrode contacts were assumed. The threshold voltages for deformations were determined by means of calculations of the phase difference Φ between ordinary and extraordinary light rays passing through a layer placed between crossed polarisers. The threshold values depended on the polarity of the bias voltage U. When the threshold value was exceeded, the phase difference increased with the voltage. Two different Φ(U/Uthreshold) dependencies for the two polarities of the voltage were found for each layer if the nematic possessed the flexoelectric properties. The possibility of using this effect to detect the flexoelectricity in the nematic was explored by simulated experiments. The effectiveness of the proposed method is discussed. 相似文献
8.
9.
The electrostatic quadrupolar interaction between spherical nematic droplets in an isotropic (and nonconducting) liquid is
calculated. It is found to have an anisotropic form U
q
∝1/R
5, where R is the distance between droplets, with repulsion for droplets having parallel orientation of the quadrupole moments and attraction
at oblique angles around the orthogonal orientation. In an external magnetic field aligning the orientations of the quadrupole
moments, a competition of the quadrupolar repulsion and van der Waals attraction (U
vdW∝ 1/R
6) leads to a specific spatial organization of droplets which is in fact often reported in experimental observations (see the
monograph by P. Drzaic, Liquid Crystal Dispersions, World Scientific, Singapore (1995) and references cited therein).
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 747–752 (25 November 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
10.
11.
We directly visualize the response and relaxation dynamics of bipolar nematic liquid crystal droplets to an applied electric field E. Despite strong planar anchoring, there is no critical field for switching. Instead, upon application of E, the surface region first reorients, followed by movement of the disclinations and the bipolar axis. After removing E, elastic forces restore the drop to its original state. The collective electro-optic properties of ordered hexagonal-close-packed monolayers of drops are probed by diffraction experiments confirming the proposed switching mechanism. 相似文献
12.
Bipolar liquid crystal drops moving inside microchannels exhibit periodic director field transformations due to induced circulating flows inside them. These modifications are characterized by changes in the type of point surface disclinations; they periodically change from splay to bend disclinations, implying the drop changes between bipolar and escaped concentric configurations. Upon stopping the flow, this structure does not relax to the lower energy bipolar configuration; we argue this is due to drop flattening inside the channels. 相似文献
13.
We developed a simple method for the calculation of the director field distribution in the droplets of nematic liquid crystals (LCs) of any shape, allowing for the interaction of LCs with the droplet surface, as well as the influence of constant electric field. In contrast to different approaches, the approach that is developed in the present paper does not require any simplifying suppositions about the structure of the LC director field. The elastic-continuum theory is used, complemented with the possibility of consideration of point and linear defects. Calculations are performed using the Monte Carlo method on a simple grid. The triangulation technique is used to take the boundary conditions of droplets of a complex shape into account. The developed approach can be used for investigation of the properties of polymer-dispersed liquid crystals (PDLCs). The topological phase transitions in the nematic LC 4-cyano-4′-pentyl-biphenyl (5CB) in spherical and ellipsoidal droplets are investigated in this paper. 相似文献
14.
Patel NM Dodge MR Zhu MH Petschek RG Rosenblatt C Prehm M Tschierske C 《Physical review letters》2004,92(1):015501
Electro-optic measurements were performed on a lamellar nematic phase in which the mesogenic moieties lie in lamellae that are separated by partially perfluorinated side groups. The twist elastic constant K22, viscosity gamma(1), and the quadratic and quartic anchoring strength coefficients are reported. K22 and gamma(1) are found to be considerably smaller than that of typical three-dimensional nematics. The small K22 is due to the greatly weakened interactions between the spatially separated lamellae. 相似文献
15.
Symmetry of a nematic liquid crystal phase is broken by an anchoring wall and also by an external field. Nematic system sandwiched
between biaxial anchoring walls is introduced as a correspondent to a bulk nematic system exposed to a couple of fields, an
electric field and a magnetic one in directions perpendicular to each other, and thermal behaviours of the system are studied.
The crossover between a homeotropic structure and homogeneous one occurs, similarly to the bulk system in the fields, in which
the anchoring condition of coexistence is shown to have the same expression as the one at the bulk. As to a characteristic
phenomenon at the sandwiched system, it is proved that an appearance of a biaxial nematic order suppresses a uniaxial nematic
order. A surface transition, i.e., a wetting phenomenon is shown to occur also in the biaxial nematics, even though the uniaxial
order is suppressed therein. 相似文献
16.
V. Yu. Rudyak M. N. Krakhalev O. O. Prishchepa V. S. Sutormin A. V. Emelyanenko V. Ya. Zyryanov 《JETP Letters》2017,105(6):384-387
Slightly diluted magnetic systems described by the disordered three-dimensional Potts model with the number of spin states q = 3 are studied in the case of a simple cubic lattice. The position of the tricritical point in the phase diagram is determined using the histogram Monte Carlo technique. 相似文献
17.
Azimuthal anchoring of a nematic liquid crystal on a grooved interface with anisotropic polar anchoring 下载免费PDF全文
Zhang Y J et al.[Zhang Y J,Zhang Z D,Zhu L Z and Xuan L 2011 Liquid Cryst.38 355] investigated the effects of finite polar anchoring on the azimuthal anchoring energy at a grooved interface,in which polar anchoring was isotropic in the local tangent plane of the surface.In this paper,we investigate the effects of both isotropic and anisotropic polar anchoring on the surface anchoring energy in the frame of Fukuda et al.’s theory.The results show that anisotropic polar anchoring strengthens the azimuthal anchoring of grooved surfaces.In the one-elastic-constant approximation(K11 = K22 = K33 = K),the surface-groove-induced azimuthal anchoring energy is entirely consistent with the result of Faetti,and it reduces to the original result of Berreman with an increase in polar anchoring.Moreover,the contribution of the surface-like elastic term to the Rapini-Papoular anchoring energy is zero. 相似文献
18.
R. Barberi I. Dozov M. Giocondo M. Iovane P. Martinot-Lagarde D. Stoenescu S. Tonchev L.V. Tsonev 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):83-91
We measure the azimuthal anchoring energy of the nematic 5CB on sinusoidal holographic unidimensional and bidimensional gratings.
We find that the anchoring strength is almost the same for all of the gratings and up to one order of magnitude stronger than
expected by the topographic mechanism proposed by Berreman. We observe strong memory effects which dominate both the elastic
anchoring and the easy axis gliding. We show that these memory effects limit from below the anchoring energy and are the main
obstacle in the realization of substrates with weak anchoring conditions.
Received: 29 April 1998 / Accepted: 23 June 1998 相似文献
19.
A new structural transition occurs at the free surface of some nematic liquid crystals when the temperature reaches a critical value T0. In this work we study the temperature dependence of the anchoring energy of the director at the free surface close to the critical point. We find that the anchoring energy tends to zero with the critical exponent δ = 1 when the temperature approaches the critical value T0. The experimental results are interpreted in terms of the Parsons and Mada theories. 相似文献
20.
The lines of constant force and the profiles of the horizontal force component are calculated for the scanning of the tip
of an atomic force microscope over a surface vacancy in a closepacked lattice with allowance for atomic displacements. The
character of the lines of force is studied in all three scanning regimes that arise for different values of the force: without
modification of the surface by the tip, migration of a single vacancy by a single interatomic distance in the direction opposite
to the motion of the tip, and “dragging” of a vacancy by the tip. It is shown that the profiles of the horizontal force component
can be used to calculate the activation energy for surface migration of a vacancy. An estimate is made of the scanning force
for which these effects may be observed experimentally.
Zh. Tekh. Fiz. 69, 104–110 (August 1999) 相似文献