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1.
The director in nematic liquid crystal cell with a weak anchoring grating substrate and a strong anchoring planar substrate is relative to the coordinates x and z. The influence of the surface geometry of the grating substrate in the cell on the director profile is numerically simulated using the two-dimensional finite-difference iterative method under the condition of one elastic constant approximation and zero driven voltage. The deepness of groove and the cell gap affect the distribution of director. For the relatively shallow groove and the relatively thick cell gap, the director is only dependent on the coordinate z. For the relatively deep groove and the relatively thin cell gap, the director must be dependent on the two coordinates x and z because of the increased elastic strain energy induced by the grating surface. 相似文献
2.
Experimental design to measure the anchoring energy on substrate surface by using the alternating-current bridge 下载免费PDF全文
The anchoring property of the substrate surface of liquid crystal cells plays an important role in display and nondisplay fields. This property directly affects the deformation of liquid crystal molecules to change the phase difference through liquid crystal cells. In this paper, a test method based on the alternating-current bridge is proposed to determine the capacitance of liquid crystal cells and thus measure the anchoring energy of the substrate surface. The anchoring energy can be obtained by comparing the capacitance–voltage curves of twisted nematic liquid crystal cells with different anchoring properties in experimental and theoretical results simulated on the basis of Frank elastic theory. Compared with the other methods to determine the anchoring energy, our proposed method requires a simple treatment of liquid crystal cells and allows easy and high-accuracy measurements, thereby expanding the test ideas on the performance parameters of liquid crystal devices. 相似文献
3.
Y. Galerne P. Hubert 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):245-249
The active oxygen gas arising from a plasma reactor is used to realize progressive chemical modifications onto silane coatings
that could be particularly interesting as alignment layers for liquid crystal display applications. Depending on the oxygen
density grafted onto the substrate, these alignment layers provide different zenithal anchoring angles, or pretilt angles,
with anchoring transitions, for polar and non-polar nematic liquid crystals as 5CB and MBBA, respectively. The anchoring transitions
are found to be smoother with the polar nematics. Such a behavior is discussed in terms of the differential wetting model
by adding a cosine term to the interaction energy between the nematic and the substrate. A local justification is proposed
for this symmetry breaking term.
Received: 18 May 1998 相似文献
4.
Liquid crystal in a nematic liquid crystal cell surface with two crossed-grating surface substrates can be oriented along the normal grating direction with given geometric parameters of groove and anchoring strength. This display is equivalent to multi-domain vertical-alignment mode. It has a relatively wide viewing angle. In this letter, we investigate the viewing angle characteristics of this kind of cell. The viewing angle dependence of contrast ratio is obtained using the extended Jones matrix method, which also considers the flexoelectric effect. The viewing angle is dependent on the geometric parameter of grating surface, the flexoelectric coefficients, and the anchoring strength. Therefore, appropriate value for each factor needs to be selected to obtain a better viewing angle of this cell. 相似文献
5.
Threshold and saturation properties of the field-induced twist cell with two parameters weak anchoring boundaries 下载免费PDF全文
On the basis of two-parameter formula of weak surface coupling anchoring
energy of nematic liquid crystals proposed by Zhao et al recently, the general
torque equilibrium equation and boundary conditions of the director have
been obtained and the threshold field as well as the saturation field of the
field-induced twist cell have been analysed for three kinds of
configurations, i.e. homogeneous, splay and Pi cells formed by
different rubbing conditions and pretilt angles. The results
indicated that the polar anchoring has no effect on the threshold field. It
is determined only by the twist anchoring and pretilt angle. But, the polar
anchoring and twist anchoring are coupling with each other and have a great
influence on the saturation field. The formulae for calculating the
threshold field and saturation field are given. These results will be very
useful in understanding surface physics and the design of liquid crystal
cells. 相似文献
6.
Daoudi A Dubois F Legrand C Laux V Buisine JM 《The European physical journal. E, Soft matter》2003,12(4):573-580
Comparative electro-optical measurements have been made on a ferroelectric liquid crystal (FLC) in surface stabilized geometry and confined to an ellipsoidal cavity within a polymer matrix. The static and dynamic electro-optical characteristics were measured for both systems and show qualitatively similar behaviours. A fast switching and important bistability were observed and characterized as a function of the applied electric field strength. The switching time between the two stable states of the surface stabilized cell was found to be longer than that found for the composite films. We argue that the faster switching dynamic of the FLC in cavities is due to the enhance of the rotational mobility of the molecules, probably (and partly) because of the soft anchoring character of the molecules at the cavity walls. Using a collective switching model in the high field regime, which assume a linear coupling between the spontaneous polarization and the local cavity electric field, we give an estimate of the rotational viscosity of the FLC molecules in the droplets.Received: 5 October 2003, Published online: 5 February 2004PACS:
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions - 77.80.Fm Switching phenomena 相似文献
7.
8.
Jin T Zalar B Lebar A Vilfan M Zumer S Finotello D 《The European physical journal. E, Soft matter》2005,16(2):159-165
Using deuteron nuclear magnetic resonance to study liquid crystals confined
to cylindrical pores, an anchoring transition has been found. The transition
exhibits an unexpected sharp dependence of the anchoring strength on
cyanobiphenyl liquid crystal molecular length. A structural transition from
a parallel axial to a planar radial configuration occurs due to an anchoring
transition from planar to weakly homeotropic orientation at the walls. The
anchoring strength is at a minimum near the decylcyanobiphenyl (10CB)
liquid crystal length. Long chain liquid crystal configurations depend on
thermal cycling and on the equilibrium atmosphere leading to a bistable SmA
structure. Orientational order wetting in the isotropic phase also depends
on molecular length. 相似文献
9.
A grating surface can drive the liquid crystal molecules to orientate
along the direction parallel or vertical to the projected plane of
the grating surface. The nematic liquid crystal (NLC) cell
manufactured with two pre-treated grating surface substrates may
realize the vertical display, parallel display and twist display. In
this paper, the threshold property of this NLC cell is investigated
systematically. With the Frank elastic theory and the equivalent
anchoring energy formula of grating surface substrate, the analytic
expressions of the threshold voltage related to three displays are
obtained, which are dependent on their geometrical parameters such
as amplitude δ and pitch λ of the grating surface
substrate. For a certain anchoring strength, the threshold voltage
increases or decreases with the increase of the value
δ/λ of the different displays. 相似文献
10.
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
11.
We discuss the peculiarity of thin nematic films on solid substrates with a free surface, underlining the differences with what is usually seen in dewetting. We review the thermodynamic basis of the coupled phase/thickness separation that has previously been shown experimentally. We give new experimental evidences for the origin of the coupling force chosen in our previous theoretical model. This additional information contributes to the discussion raised by the article of Ziherl and Zumer in this issue [19].Received: 3 December 2003PACS:
68.15. + e Liquid thin films - 64.70.Md Transitions in liquid crystals - 61.30 Surface phenomena in liquid crystals including anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions and wetting transitions 相似文献
12.
The effect of a surface electric field produced by ionic adsorption on the molecular orientation of a nematic liquid crystal
sample is analyzed. The eigenvalue problem for a semi-infinite medium is analytically solved both for strong and weak anchoring
situations. The threshold instabilities are numerically determined and it is shown that the homeotropic pattern can be destabilized
also in the situation of strong anchoring. The dependence of the threshold field on the anchoring strength and on the surface
polarization is determined by taking into account also the coupling of the quadrupolar component of the flexoelectric coefficient
with the field gradient.
Received 4 November 1999 and Received in final form 4 April 2000 相似文献
13.
We report on first studies of wetting of liquid crystal on photoaligning surface. We observed strong light-induced variations
of a contact angle of a liquid LC 5CB on a photoaligning surface of fluoro-polyvinyl-cinnamate (PVCN-F) and we connected these
variations with changes of PVCN-F polarity. We also present drastic changes of the contact angle of a nematic liquid crystal
(MLC-6080) on the PVCN-F surface in a vicinity of temperature anchoring transition of liquid crystal from homeotropic orientation
to planar one. We did not find any peculiarities in temperature dependence of the contact angle of isotropic liquid (glycerol)
on PVCN-F and of nematic liquid crystal on pure glass in the same temperature range. It allows us to suggest that rearrangement
of LC molecules and flexible fragments in the LC-polymer interface are responsible for the change of surface tensions both
of LC and polymer and the observed jump of the contact angle. 相似文献
14.
受自然界启发,仿生微结构被广泛用于调控固-液界面的性质.研究显示,液滴在微结构表面的各向异性浸润行为可用于实现微流动方向和速度的控制,且其各向异性浸润与微结构的尺寸和分布等密切相关.本文研究了微矩形凹槽尺寸对液滴各向异性浸润行为的影响规律.结果显示,液滴沿平行沟槽的方向具有较小的运动阻力、易铺展,因此具有较小接触角;而垂直于沟槽方向,由于沟槽的阻隔作用具有较大运动阻力,因而具有较大接触角,并且在垂直方向液滴的浸润过程是三相线一系列钉扎和跳跃行为.在微矩形凹槽表面,液滴沿平行方向接触角θ//与肋板宽度R和凹槽宽度G密切相关,其值与表面固体面积比成反比;而垂直于沟槽方向的接触角θ⊥随肋板宽度R和凹槽宽度G变化基本保持不变.同时各向异性液滴的变形比L/W、特征方向接触角比值θ⊥/θ//与表面固体面积比成正比.研究结果有助于加深理解微结构表面浸润行为的机制,并为微矩形凹槽在微流动控制方向的应用提供技术支持. 相似文献
15.
The anchoring properties of substrate with a grating surface are
investigated analytically. The alignment of nematic liquid
crystal (NLC) in a grating surface originates from two
mechanisms, thus the anchoring energy consists of two parts. One
originates from the interaction potential between NLC molecules
and the molecules on the substrate surface, and the other stems
from the increased elastic strain energy. Based on the two
mechanisms, the expression of anchoring energy per unit area of
a projected plane of this grating surface is deduced and called
the equivalent anchoring energy formula. Both the strength and
the easy direction of equivalent anchoring energy are a function
of the geometrical parameters (amplitude and pitch) of a grating
surface. By using this formula, the grating surface can be
replaced by its projected plane and its anchoring properties can
be described by the equivalent anchoring energy formula. 相似文献
16.
Hydrodynamics of planar nematic liquid crystal molecules under the influence of horizontal pressure gradient was studied, theoretically. The pressure gradient is due to nematic liquid crystal volume expansion which is a consequence of the incompressibility of the liquid. The resulting director reorientation which is due to coupling between the director orientation and fluidity of the liquid is calculated numerically for the hard and weak anchoring conditions at the cell walls. 相似文献
17.
First-order Fréedericksz transition at the threshold point for weak anchoring nematic liquid crystal cell under external electric and magnetic fields 总被引:1,自引:0,他引:1 下载免费PDF全文
Based on the modified formula of Rapini-Papoular, the equilibrium equation and boundary condition of the director have been obtained and the behaviour of the Fréedericksz transition at the threshold point has been studied for weak-anchoring nematic liquid crystal cells under external electric and magnetic fields with the methods of analytical derivation and numerical calculation. The results show that, except for the usual second-order transition, the first-order Fréedericksz transition can also be induced by a suitable surface anchoring technique for the liquid crystal cell given in the paper. The conditions for the existence of the first-order Fréedericksz transition are obtained. They are related to the material elastic coefficient k_{11}, k_{33} the thickness of the liquid crystal cell, the external electric field and the strength of surface anchoring, etc. 相似文献
18.
理论分析和数值模拟相结合,研究了表面序电极化、挠曲电极化对非对称弱锚定向列液晶盒在饱和点双稳态的影响,得到了两种极化共存时液晶指向矢满足的方程和边界条件.通过引入新的状态参量,从能量的角度对两种极化的物理效应进行了分析.结果表明,在一定条件下,两种极化耦合,在饱和点通过改变锚定能影响边界条件,从而诱导双稳态.文中给出了判断是否存在双稳态的一般条件,此条件与数值计算结果符合.
关键词:
表面序电极化
挠曲电极化
饱和点
双稳态 相似文献
19.
The confining effect of a spherical substrate inducing anchoring (normal to the surface) on rod-like liquid crystal molecules contained in a thin film spread over it has been investigated with regard to possible changes in the nature of the isotropic-to-nematic phase transition as the sample is cooled. The focus of these Monte Carlo simulations is to study the competing effects of the homeotropic anchoring due to the surface inducing orientational ordering in the radial direction and the inherent uniaxial order promoted by the intermolecular interactions. By adopting an entropic sampling procedure, we could investigate this transition with a high temperature precision, and we studied the effect of the surface anchoring strength on the phase diagram for a specifically chosen geometry. We find that there is a threshold anchoring strength of the surface below which uniaxial nematic phase results, and above which the isotropic fluid cools to a radially ordered nematic phase, besides of course expected changes in the phase transition temperature with the anchoring strength. In the vicinity of the threshold anchoring strength we observe a bistable region between these two structures, clearly brought out by the characteristics of the corresponding microstates constituting the entropic ensemble. 相似文献
20.
To account for azimuthal surface anchoring of a nematic liquid crystal, Berreman [Phys. Rev. Lett. 28, 1683 (1972)10.1103/PhysRevLett.28.1683] proposed a simple model attributing the surface anchoring to the elastic distortion of the liquid crystal induced by the grooves of a surface. He showed that the surface anchoring energy is proportional to sin(2)varphi, with varphi being the angle between the director at infinity and the direction of the surface grooves. We argue that his assumption of negligibly small azimuthal distortion of the nematic is not valid. Proper treatment of the azimuthal distortion reveals that the Berreman's model should yield a surface anchoring energy proportional to sin(4)varphi. This implies that surface grooves alone cannot contribute to the surface anchoring coefficient in the usual Rapini-Papoular sense. 相似文献