Rubbed polyimide

Fig. 3.85 (a) Schematic of the polyimide rubbing process TM-AFM height images (z-scale 3 nm) of (b) the pristine polyimide film, and (c) and (d) a rubbed film. The rub direction in (c) was from upper left to lower right, in (d) vertical. Reprinted with permission of John Wiley Sons, Inc. from [176]. Copyright 2001. John Wiley Sons, Inc. 

Fig. 2.37 Rubbing strength and pretilt angle relations of two types of polyimide ( -A, x-B polyimide) rubbing strength represents the offset height from the standard position.

Cell number Type of polyimide Rubbing direction... 

Distortions of the bond and out-of-plan rotation of polyimides have been suggested to explain the surface modification by rubbing.33... 

NAJM Van Aerie, M Barmentlo, and RWJ Hollering, Effect of rubbing on the molecular orientation within polyimide orienting layers of liquid-crystal displays, J. Appl. Phys., 74 3111-3120, 1993. 

Electro-optic effects induced by doping liquid crystals with one-dimensional metal nanoparticles were not only investigated in standard electro-optic test cells, but also in costume-made cells consisting of a thin layer of liquid crystal either deposited onto a thin film of alumina with embedded GNRs [443], or using rubbed polyimide alignment layers modified with solution-cast GNR [444]. In both cases, surface plasmon resonance frequencies of the GNR integrated into these liquid crystal cells could be electrically controlled. 

A standard TN-LCD consists of a nematic liquid crystal mixture of positive dielectric anisotropy contained in a cell with an alignment layer on both substrate surfaces, usually rubbed polyimide, crossed polarisers and a cell gap of 5- 0fim, see Figure 3.7. The nematic director is aligned parallel to the direction of rubbing in the azimuthal plane of the device. The alignment layer induces a small pretilt angle (6 1-3°) of the director in the zenithal plane. The... 

ZnTPP was synthesized in our laboratory and characterized by UV-vis, EA, H-NMR, IR, MS and 5CB was from BDH (as shown in Figure 1). Two samples were studied in the experiment, 5CB and 5Cb doped with 1% (w/w) ZnTPP. The samples were sandwiched between two glass substrates with 23.6pm spacers, the two glass substrates were coated with polyimide and rubbed unidirectionally to give planar alignment. 

It was observed that the liquid crystalline substances incorporated on the polyimide films which were only 0.8 nm (2 layers) thick were successfully oriented to the transfer direction without a surface rubbing treatment of the polyimide film. This observation can be explained by orientation of the polymer molecule to the film transfer direction as observed by polarized UV and IR spectroscopy. 

Hopkins and Campbell used Dual Rub-Shoe and Falex test machines to study the wear lives of a series of polyimide-bonded molybdenum disulphide coatings, with initial coating thicknesses varying from 2.5 //m to 25 yi/m. Both test machines use line contact, and they calculated the initial contact zone stresses as 276 MPa and 669MPa respectively, reducing to 103 MPa and 171 MPa by the end of testing. They... 

Figure 7 (left) The electric field dependence of the time-ofiflight hole mobility for poly(9.9-dioctylfluorene) films. The open circles are data for a film prepared by spin coating. The filled circles are for a sample spin coated on a rubbed polyimide orientation layer, annealed in the nematic phase and then quenched to form a glassy film. 

FIGURE 10.19. Polarized absorption spectra for a film of PF2/6 oriented on a rubbed polyimide alignment layer. The spectra were measured for light polarized parallel (filled circles) and perpendicular (open circles) to the rubbing direction. (From Ref. 4.)... 

In contrast the polymer 19 with branched alkyl chains displays only one nematic phase. Thus 19 shows a phase transition at 167 °C upon heating with the reverse transition upon cooling being seen at 132 °C. Annealing of a film of 19 at 185 °C upon a rubbing-aligned polyimide layer followed by rapid... 

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