共查询到20条相似文献,搜索用时 0 毫秒
1.
By use of a local stability criterion recently introduced, we predict the existence of a periodic saddle-splay Freedericksz (PSSF) transition that adds to the existing class of classical Freedericksz transitions driven in a nematic cell by an external field. Occurrence of the PSSF transition requires a saddle-splay elastic constant with a large enough magnitude and different anchoring strengths at the plates confining the nematic cell. Otherwise, either the PSSF transition does not occur at all, or it requires a field higher than that associated with the classical aperiodic splay Freedericksz (ASF) transition, in which case it is not observable. Here, we determine the threshold field for which the PSSF precedes the ASF transition, as well as the structure of the destabilizing mode. 相似文献
2.
Gabriela Iacobescu Adrian Liviu Păun Cristina Cârtoaje 《Journal of magnetism and magnetic materials》2008
A static and dynamic investigation was performed on liquid crystal cells containing pure nematics and nematics doped with an azo-dye (Methyl Orange). It was found that the critical field for magnetic Freedericksz transition was decreased in samples containing the “trans” isomer and increased in those containing the “cis ” isomer. Changes in the relaxation time τA, τB intervening when switching on/off the magnetic field were also noticed. A theoretical model was elaborated to explain these phenomena. 相似文献
3.
A new theoretical approach was elaborated to explain the contradictions reported in many papers about the electric threshold for Freedericksz transition in nematic liquid crystal (NLC) with ferroparticles additives. The free energy density of the mixture was estimated and the contributions of the interaction energy of NLC molecules with ferroparticles surface were calculated. Experimental results for 5CB-BaTiO3 mixture are given. 相似文献
4.
Lin Ziyang Jue Shi Xiang Ying L. P. Shi Wang Jian Z. X. Liang Z. R. Qiu 《Physics letters. A》2000,270(6):207-330
We observed an azo-isomerization-induced Freedericksz transition of the 5CB liquid crystal doped with 1% double-azo. In experiment, we found that the Freedericksz transition threshold occurred at optical intensity level of 0.3 mW/mm2 for the 12.5 μm-thickness planar alignment doped 5CB, which is four orders of magnitude lower as that for the pure 5CB. Using optical phase retardation, we measured the relations between the Freedericksz transition threshold and the pump beam polarization. The maximum twist angle of liquid crystal molecules under different pump beam intensity is given. The experiment indicated that trans–cis isomerization plays an important role in the decrease of the Freedericksz transition threshold. 相似文献
5.
A. A. Ghandevosyan R. S. Hakobyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2012,47(1):33-35
A phenomenological theory of electric Freedericksz transition in planar-oriented nematic liquid crystals doped with spherical
ferroelectric nanoparticles is considered. It is shown that even spherical nanoparticles can critically reduce the threshold
of Freedericksz transition, due to their ability to strongly increase the electric field in the medium. At higher values of
polarization and concentration of nanoparticles a Freedericksz transition without threshold can occur. In this case only an
insignificant electric field needs for orienting the nanoparticles. 相似文献
6.
V. I. Tsoy 《Technical Physics》2002,47(1):34-37
The bistability of a nematic liquid crystal layer with the asymmetric directions of easy orientation and weak orientational anchoring is considered within the framework of the continuum theory. The feasibility of passive storage applications based on two differing states of lateral bending is demonstrated. Switching between these splay states does not require the motion of the domain walls and can be accomplished by the two-frequency control of the low electric field applied to the crystal. 相似文献
7.
8.
《Physics letters. A》2006,357(2):159-162
In this Letter, we studied the optical-induced Freedericksz transition of 5CB doped with 1% volume fraction of bio-molecule, porphyrinozinc(II) (ZnTPP). Excited by Ti:sappire laser with the 82 MHz repetition rate and 100 fs pulse duration, the optical Freedericksz threshold of a 23.6 μm-thickness planar alignment sample occurred at an intensity level of 0.35 mW/mm2 in contrast to the normally observed 83 mW/mm2 value for pure 5CB. 相似文献
9.
Caggioni M Roshi A Barjami S Mantegazza F Iannacchione GS Bellini T 《Physical review letters》2004,93(12):127801
We present a high-resolution study of the isotropic to nematic phase transition of a low birefringence liquid-crystal compound incorporating an aerosil gel. Calorimetry, light scattering, and microscopy data coherently combine to allow for an accurate determination of the temperature dependence of the onset of the nematic state. The nematic order develops on cooling through two distinct processes while the nematic correlation length mildly decreases. We understand the doubling of the phase transition as due to a crossover from a random-dilution regime, where the silica gel couples to the scalar part of the nematic order parameter, to a low-T random-field regime, where the coupling induces distortions in the director field. 相似文献
10.
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
11.
Zhang S Wen B Keast SS Neubert ME Taylor PL Rosenblatt C 《Physical review letters》2000,84(18):4140-4143
It is shown experimentally that a very-long-pitch, surface-stabilized, anticlinic liquid crystal undergoes a two-step electric-field-induced transition to the synclinic phase. The liquid crystal remains undistorted below a threshold field E(th). For E>E(th), a Freedericksz transition occurs, wherein molecules in adjacent smectic layers undergo unequal azimuthal rotations about the layer normal. At higher fields a transition to the synclinic phase occurs via solitary waves. 相似文献
12.
Lucchetta DE Scaramuzza N Strangi G Versace C 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):610-612
In this paper, a study of the electrically driven turbulent-turbulent transition in a homeotropically oriented nematic sample is reported. The transition has the characteristics of a nucleation process, and its threshold has been experimentally determined. The nucleation rate and the growth velocity of the new turbulent nuclei are also reported. 相似文献
13.
O. A. Kapustina 《Acoustical Physics》2006,52(4):413-417
The adequacy of the new theoretical model based on the ideas of nonequilibrium thermodynamics and nonlinear hydrodynamics of liquid crystals for describing the mechanism of threshold reorientation of molecules in a homeotropically oriented layer of a nematic liquid crystal under the effect of a cross-homogeneous ultrasonic wave is experimentally substantiated. It is demonstrated that (i) the critical particle velocity is inversely proportional to the layer thickness, (ii) its relation to the frequency of oscillations is ambiguous and depends on the relation between the ultrasonic frequency and the inverse relaxation time of the orientation order parameter, and (iii) the stationary distortion of microstructure is homogeneous along the layer. 相似文献
14.
15.
16.
The paper reports new nematic liquid crystals that are paramagnetic. 相似文献
17.
18.
Thermomechanical mechanism of the director reorientation in twisted nematic liquid crystals caused by the one-dimensional longitudinal temperature gradient is predicted and studied theoretically. The calculated director reorientations are in the range that can be measured experimentally very easily. 相似文献
19.
S. Marčelja 《Solid State Communications》1973,13(7):759-762
The ordering of hydrocarbon end-chains in nematic liquid crystals has been calculated by numerical summation over all chain configurations in the molecular field. The results, used in a self-consistent calculation of the orientational ordering for the full system, explain the variation of the isotropic-nematic transition temperatures (including the even-odd effect) and transition entropies with end-chain length. 相似文献
20.
A. Humpert A.J. Masters M.P. Allen 《The European physical journal. Special topics》2016,225(8-9):1723-1732
We examine the behaviour of single-particle orientational time correlation functions in nematic liquid crystals. As well as the expected dynamics involving oscillation in a mean-field potential, and occasional jumps between orientations parallel and antiparallel to the director, we provide the first simulation evidence of long-time tails characteristic of coupling to director fluctuations. 相似文献