Alignment of liquid crystals

Liquid Crystal Displays (LCD). Liquid crystal displays, once limited to small devices such as calculators, are now displacing color CRT (cathode ray tube) displays in commercial quantities. The ability to fabricate these display devices at high quality and at low cost is partially due to the wider spread use of photopolymer-based materials. Photopolymer technology is being used for the alignment of liquid crystal (LC) elements (49), the orientation of ferroelectric materials (50), the synthesis of LC polymers (57) and the manufacture of color filters for liquid crystal display applications (52). 

Title Photosensitive Polyimides for Optical Alignment of Liquid Crystals... 

Schadt, M., Schmit, K., Kozenkov, V., and Chigrinov, V. Surface-induced parallel alignment of liquid crystals by linearly polymerized photopolymers. Jpn, J. Appl. Phys. 31, 2155 (1992). 

Figure 3.89. Normalized TP fluorescence intensity of polymer dispersed liquid crystals as a function of the polarization angle of the reading beam, which is defined as the angle between the writing and reading polarization states. Inset top Schematic alignment of liquid crystal directors in exposed (dots) and unexposed regions. Inset bottom Two fluorescing data bits obtained by irradiation at a polarization angle of 90°. (From Ref. [248] with permission of the American Institute of Physics.)...

Gupta, V.K. Abbott, N.L. Design of surfaces for patterned alignment of liquid crystals on planar and curved substrates. Science 1997,276, 1533-1536. 

Table 5. Parameters characterizing the macroscopic alignment of liquid crystal side diain polymers and low molecular weight analogues ...

Fig. 5.8 Alignment of liquid-crystal copolymer MACB-CNB6 upon 30 min of exposure to polarized light at 2=366 nm (2.8 mWcm" ) at 106°C. (a) Transmittance of probe light (633 nm) through a 2 pm thick copolymer film placed between crossed polarizers as a function of the rotation angle, (b) Experimental set-up. Adapted from Wu et al. [45] with permission from Elsevier.

Since the pioneering work on surface-induced alignment of liquid crystals, performed by Lehmann [1], Grandjean [2], Mauguin [3], Chatelain [4], and others [5], scientist have been looking for the answer to the question why do certain surfaces align liquid crystals and others not ... 

The answer to this question has become even more important with the advent of modern liquid crystal display technologies, that are based on reliable and technologically controllable surface alignment of liquid crystals, used in a variety of electrooptic devices, such as liquid crystal displays, light modulators, optical shutters, switches, holographic systems, etc. 

In this Chapter we want to introduce some basic concepts and present an overview of the mechanisms, that are in our opinion responsible for the alignment of liquid crystals on solid and soft-matter interfaces. In addition we will present and discuss recent developments and results in surface sensitive... 

It is well known from the early work on surface alignment of liquid crystals [5] that glass surface covered with N,N — dimethyl — N — octadecyl — 3 — aminopropyltrimethoxysilyl chloride DMOAP) orients liquid crystal molecules perpendicularly to the glass surface. The quality of alignment is ex-... 

As discussed in Chapter 1, photo-polymers that have been unidirectionally modified by exposure to linearly polarized light have the ability to induce alignment of liquid crystals [37-41]. This works presumably via anisotropic van der Waals forces [38], similar to the alignment on conventionally rubbed polymer layers [18,22]. In spite of this similarity, generally there are large differences found between the surface anchoring strengths of these two types of... 

Optical properties of organic compounds are determined by the polarization of electrons along the induced electric field. On the other hand, photochemical reactions change the chemical structures and electronic states of organic materials. Many researchers are interested in photoisomerization of azo dyes because it changes orientations of dye molecules and can be controlled with light irradiation. This effect is utilized for optically-induced alignment of liquid crystals(i, 2) and... 

Polymer Network Stabilized Liquid Crystal Displays. The alignment of liquid crystals plays an important role in the operation of a display. The alignment is conventionally induced by the display cell surfaces, but by distributing the surface of a polymer network through out the bulk of the liquid crystal, new properties are possible, and the performance of conventional devices can be improved. This short section will mention some of the conventional liquid crystal display devices modified by these polymer networks. 

B. W. Lee, N. A. Clark, Alignment of liquid crystals with patterned isotropic surfaces. Science 291, 2576-2580 (2001)... 

Fig. 7.7 Schematic device configuration for alignment of liquid crystals by oscillating shear. POM photographs of aligned sample are shown below, the bidirectional shear direction is indicated by the dotted arrow. Reproduced with permission from [137]. Copyright 2013 The Japan Society of Applied Physics...

Thermally switched liquid crystal alignments can be obtained with a rubbed PVK film [70]. A mechanically rubbed PVK layer can induce a planar alignment of liquid crystals with their axis direction perpendicular to the direction of rubbing. This direction can be switched toward the rubbing direction by a thermal treatment. A possible application of such a device is for polarization rotators. The PVK film does... 

Alternatively, the method for producing uniform liquid crystal alignment in a liquid crystal cell comprises the steps of providing a substrate, and printing at least one layer of a polymer ink solution onto the substrate with a printer to form a printed pol mier ink layer having a predetermined thickness. Air is then blown upon the printed polymer ink layer to produce induced anisotropy on the printed pol mier ink layer. Using the substrate in a liquid crystal cell provides alignment of liquid crystals in the liquid crystal cell (26). 

T. Uchida, Surface alignment of liquid crystals, in Liquid crystals-applications and uses, Vol. 3, ed. B. Bahadur (World Scientific, New Jersey, 1990). 

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