Liquid Crystal Alignment

SAMs are generating attention for numerous potential uses ranging from chromatography [SO] to substrates for liquid crystal alignment [SI]. Most attention has been focused on future application as nonlinear optical devices [49] however, their use to control electron transfer at electrochemical surfaces has already been realized [S2], In addition, they provide ideal model surfaces for studies of protein adsorption [S3]. 

An essential requirement for device applications is that the orientation of the molecules at the cell boundaries be controllable. At present there are many techniques used to control liquid crystal alignment which involve either chemical or mechanical means. However the relative importance of these two is uncertain and the molecular origin of liquid crystal anchoring remains unclear. Phenomenological models invoke a surface anchoring energy which depends on the so-called surface director , fij. In the case where there exists cylindrical symmetry about a preferred direction, hp the potential is usually expressed in the form of Rapini and Popoular [48]... 

Figure 2.2 The transparent electrodes in an LCD are coated with crossed polarizers. The liquid crystals (depicted as slender lozenges) form helices, thereby guiding polarized light from the upper electrode through the LCD, enabling transmission through to the lower polarizer. This is why the display has no colour. The helical structure is destroyed when a voltage is applied, because the polar liquid crystals align with the electrodes field. No light can transmit, so the display looks black...

K. Ichimura, Photoregulation of liquid crystal alignment induced by polarization photochromism of molecular films, Mol. Cryst. Liq. Cryst., 246, 331-338 (1994). 

Title Diamines, Polyimide Precursors, and Polyimides Produced by Using the Diamines and Liquid Crystal Aligning Agents... 

Poly(amic acids) were prepared by the ambient temperature condensation of 1,2,3,4-cyclobutane tetracarboxylic dianhydride with selected aromatic diamines. When the poly(amic acids) and liquid crystal alignment agents y-butyrolactone and A-methyl-pyrrolidone were spin-coated and cured onto an inert surface, the polyimide was effective as a liquid crystal aligner. 

Preparation of Mixed Polyimides as Liquid Crystal Aligning Films... 

TABLE 2. Physical properties of polyimides as liquid crystal aligning films prepared by heating A-methyl-pyrrolidone and y-butyrolactone, 8 2, respectively, with polyamic acids described in Table 1. 

Photo-crosslinkable malimide (VII) and styryl (VIII) derivatives were prepared by Nakata [3] and used as liquid crystal aligning agents and liquid crystal display elements. 

Polyimides derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride and selected aromatic diamines have been found effective as photosensitive materials. These materials have applications as liquid crystals aligners, liquid crystal displays, and related liquid crystal optical elements. The fdm preparation uses a noncontact method that can reduce dust and static charge buildup and improve resolution. 

In a subsequent investigation by the author [1] additional Step 5 products, (I) and (II), were prepared and used in liquid crystal alignment layers. 

The preparation of other aromatic diamines, (III), useful in preparing photosensitive polyimides effective as liquid crystal alignment agents is provided by the author [2]. 

Polyimides derived from diamines containing a steroid component, (V), were prepared by Hiraoka [4] and used as method for producing liquid crystal alignment layers. 

K. Ichimura, K. Photoalignment of Liquid-Crystal Systems. Chem. Rev. 100, 1847 (2000). Ichimura, K., Seki, T, Kawanishi, Y., Suzuki, Y., Sakuragi, M., and Tamaki, T. Photocontrol of Liquid Crystal Alignment by Command Surfaces , in Photoreactive Materials for Ultrahigh Density Optical Memory. M. Irie, Ed., Elsevier Amsterdam, (1994), p. 55. 

Li, X. X, Natansohn, A., and Rochon, P. Photoinduced liquid crystal alignment based on a surface relief grating in an assembled cell. Appl. Phys. Lett. 1999, 74, pp. 3791-3793,... 

Kim, D. Y., Kumar, J., and Tripathy, S. K. Liquid crystal alignment using optically induced surface relief gratings on azo polymer films. Polymer Preprints 1998, 319, pp. 1107-1108. 

SURFACE PHOTOCHROMISM FOR REGULATION OF LIQUID-CRYSTAL ALIGNMENT... 

Surface-Assisted Liquid-Crystal Alignment Control... 

Using these novel LB films, systematic studies have been carried out to elucidate which features of the molecular structures of azo chromophores govern the photoinduced switching of the liquid-crystal alignment.165-169 The effects of spacer length (n) and tail length (m + 1) on the photoresponse of liquid-crystal... 

K. Ichimura, H. Akiyama, K. Kudo, N. Ishizuki, and S. Yamamura, Command surfaces 12. Factors affecting in-plane photoregulation of liquid crystal alignment by surface azobenzenes on a silica substrate, Liq. Cryst. 20, 423 435 (1996). 

T. Seki, M. Sakuragi, Y. Kawanishi, Y. Suzuki, T. Tamaki, R. Fukuda, and K. Ichimura, Command surface of Langmuir-Blodgett films. Photoregulation of liquid crystal alignment by molecularly tailored surface azobenzene layers, Langmuir 9, 211-218 (1993). 

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