Nematic hybrid aligned - cell

It has also been used to study the second sound resonance in smectic A liquid crystals and measure the compression modulus. For measuring the flexocoefficients (ei — 63) and (ei + 63), hybrid-aligned nematic cells have been used extensively. AC techniques avoid problems associated with ionic impurities, but require elaborate numerical fitting of the data. Some observations on the pnblished measurements of flexo-coefHcients are made in Section 2.4, which ends with a few concluding remarks. 

Fig. 2.2. Schematic diagram of a hybrid-aligned nematic cell. The field-free director (shown by the continuous curved line) has a splay-bend curvature distortion in the xz plane. A DC field applied along the y axis rotates the polarization and the director (shown by the curved dashed line) acquires a 4>(z) profile. (Reproduced from Dozov et al. with the permission of EDP Sciences, http //publications.edpsciences.org.)...

S.A. Jewell and J.R. Sambles, Fully leaky guided mode study of the flexoelectric effect and surface polarization in hybrid aligned nematic cells, J. Appl. Phys. 92(1), 19-24, (2002). doi 10.1063/1.1483392... 

P.R. Maheswara Murthy, V.A. Raghunathan and N.V. Madhusudana, An AC electro-optic technique of comparing the two anchoring energies of a hybrid aligned nematic cell, Liq. Cryst. 14(4), 1107-1124, (1993). 

A. Mazzulla, F. Ciuchi and J.R. Sambles, Optical determination of flexoelectric coefficients and surface polarization in a hybrid aligned nematic cell, Phys. Rev. E 64(2), 021708/1-6, (2001). doi 10.1103/PhysRevE.64.021708... 

Guillen, A.D. Mendoza, C.I. (2007). Influence of an electric field on the non-Newtonian response of a hybrid-aligned nematic cell under shear flow. The Journal of Chemical Physics, Vol. 126, pp. 204905-1-204905-9 Guillen, A.D. Mendoza, C.I. (2007). Erratum Influence of an electric field on the non-Newtonian response of a hybrid-aligned nematic cell under shear flow. The Journal of Chemical Physics, Vol. 127, pp. 059901-1-059901-2... 

C.-W. Kuo, S.-C. Jeng, H.-L. Wang, C-.C. Liao, Application of nanoparticle-induced vertical alignment in hybrid-aligned nematic liquid crystal cell. Appl. Phys. Lett. 91, 141103 (2007)... 

N.V. Madhusudana and G. Durand, Linear flexo-electro-optic effect in a hybrid aligned nematic liquid crystal cell, J. Physique Lett. 46(5), L-195-L-200, (1985). doi 10.1051/jphyslet 01985004605019500... 

N.T. Kirkman, T. Stirner and W.E. Hagston, Continuum modelling of hybrid-aligned nematic liquid crystal cells optical response and flexoelectricity-induced voltage shift, Liq. Cryst. 30(9), 1115-1122, (2003). doi 10.1080/02678290310001594562... 

T.S. Taphouse, S.L. Cornford, J.E. Birkett and J.R. Sambles, Time-resolved sign-dependent switching in a hybrid aligned nematic liquid crystal cell. New J. Phys. 10(8), 083045/1-15, (2008). 

FIG. 1. Schematic representation of the hybrid aligned nematic (HAN) cell with no applied field. The rod lines show the alignment of the director n at different points in the cell. 

The flexoelectric distortion in Hybrid Aligned Nematic (HAN) configuration was studied [190, 191]. In HAN cells the director is homeotropic on one of the substrates and homogeneous on the other. The measme-ments of transmitted intensity in HAN samples allow us to evaluate for MBBA both a nematic anchoring energy W for the homeotropic orientation VF 6 X 10 erg/cm and the sum of the flexoelectric moduli 11 + 33 —4.5 X 10 dyn / [191]- In an electric field normal to the initial director plane, the flexoelectric effect results in the appearance of twist deformation, observed by the rotation of linearly polarized light [190]. 

G. Barbero and R. Barberi, Critical thickness of a hybrid aligned nematic liquid crystal cell,/. Phys., 44, 609 [1983]. 

On the other hand, if the molecules are not strongly anchored to the boundary, that is, the so-called soft-boundary condition (Fig. 3.3), an applied field will perturb the orientation of the molecules at the cell boundaries. In this case a quantitative description of the dynamics of the field-induced effects must account for these surface energy terms. A good account of surface energy interaction may be found in the work of Barbero et al.," which treats the case of optical field-induced effects in a hybrid aligned nematic liquid crystal cell. 

Figure 5.22 The transflective LCD configuration with a single cell gap. Compensation films are optimized for a particular LC electro-optic mode, such as TN or hybrid aligned nematic (HAN) [28]. Reproduced from H. Y. Mak, P. Xu, V. G. Chigrinov, and H.-S. Kwok, Novel single cell gap hybrid aligned nematic transflective LCD. ASID34, ASID 07 Cottference, Singapore (2007), The Society for Information Display...

H. Y. Mak, P. Xu, V. G. Chigrinov, and H.-S. Kwok, Novel single cell gap hybrid aligned nematic transflective LCD. ASID34, ASID 07 Cortference, Singapore (2007). 

Fig. 8.9. (a) Director s tilt angle with respect to the 2 direction in a /i = 10-layer hybrid nematic cell as a function of MG temperature. Different lines correspond to the tilt angle in distinct layers 1 denotes the LG layer closest to the in-plane aligning substrate and 10 the layer nearest to the homeotropic substrate. Inset Temperature variation of ordering parameters in the two layers closest to the middle of the cell, (b) Temperature of the structural transition as a function of a cell thickness. 

Fig. 8.19 Walls. Hybrid nematic cell with planar and homeotropic director alignment at opposite bovmdaries with a wall between the two degenerate patterns differing by a tilt angle sign (a), and the top view on the different tilt areas surrounded by walls (b)...

FIGURE 4.3. The Prederiks transition in different geometries (a) nematic between two coaxial cylinders (b) quasi-homeotropic orientation with opposite director tilt at the boundaries and (c) hybrid aligned (homeoplanar) nematic cell. 

Several types of spontaneous periodic director pattern yield information about elastic coefficients. Static stripe textures, as described by Lonberg and Meyer [45], appear in polymer nematics if the twist/splay ratio below the critical value of 0.303. Calculations of director fields and the influence of elastic constants and external fields on the appearance of these periodic patterns have been performed by several authors (e.g. [49-51]). In nematic cells with different anchoring conditions at the upper and lower cell plates (hybrid cells), other types of striped texture appear these are similar in nature, but involve different director deformations and elastic coefficients. For a description of various types of static periodic texture and their relationship to elastic coefficients see, for example, Lavren-tovich and Pergamenshchik [52]. In thin hybrid aligned films, a critical thickness is observed below which the director align-... 

To realize the concept described in Sect. 4.2, we reasoned that the nematic rodlike liquid crystal cell needs a nematic discotic liquid crystal with hybrid alignment as a compensator. 

Besides these two standard cell alignments, there are many other variations such as hybrid, twisted, supertwisted, fingerprint, multidomain vertically aligned, etc. Industrial processing of these nematic cells, as well as the transparent conductive coating of the cell windows for electro-optical device applications, is understandably more elaborate. 

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