Unidirectionally rubbed

A glass slide (ca. 1cm X 1 cm) is spin-coated with a solution of Probimide 32 in dimethylformamide. The coated slide is annealed at high temperatures (ca. 200°C), followed by unidirectional rubbing with a soft cloth, to yield a hard, inert, rubbed polymer film, suitable for enticing homogeneous alignment of a mesophase. 

Fig. 10.19 A mechanical nano-relief obtained as a result of unidirectional rubbing the polymer surface long polymer molecules are schematically represented by ellipsoids...

FIGURE 2 Pretilted surface alignment of the director by unidirectional rubbing of a polymer layer. 

Zocher stated that uniform parallel alignment could be obtained if the cell surfaces were first unidirectionally rubbed. Various materials such as paper, tissue, and cotton wool were used to achieve uniform parallel alignment. Chatelain hypothesized that the parallel orientation resulted from the forces generated by the presence of an adsorbed layer of fatty contaminants on the cell surface, and the directionality was achieved by the unidirectional rubbing However, he could not eliminate the possibility that mechanical deformation of surface might have induced the observed alignment. 

R. Yamaguchi, Y. Goto, and S. Sato, Liquid crystal alignment surface with two easy axes induced by unidirectional rubbing. Applied Physics Letters 82, 4450 (2003). 

Oils may act in two ways they provide a measure of boundary lubrication and they may exclude oxygen from the rubbing zone. However, their effectiveness is not as great as with unidirectional sliding, since there is usually sufficient oxygen present in most cases to allow oxide debris to be generated, and this tends to displace any lubricant film that was initially present between the surfaces. 

Inflated Diaphragm Method (ASTMD3886). This method is applicable both to woven and knitted fabrics. The specimen is abraded by rubbing either unidirectionally or multidirectionally against an abradant having specified surface characteristics. The specimen is supported by an inflated rubber diaphragm under a constant pressure. Evaluation of abrasion resistance can be either by determination of the number of cycles required to wear through the center of the fabric completely or by visual examination of the specimens after a specified number of cycles. 

Most (but not all) LCDs require that the liquid crystal be uniformly oriented i.e., that the LC exist in the form of a single domain in either the OFF or ON condition. The required alignment can be brought about by imparting to the confining surfaces a unidirectional sense, either by rubbing or by the oblique evaporation of SiO or other compounds (Kahn, 1977). A variety of boundary conditions can therefore be set up, including some that result in a metastable behavior of the enclosed liquid crystal phase. 

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. 

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... 

Unfortunately, the ideal bookshelf structure is difficult to make. Usually the electrodes are covered by polymer layers and rubbed unidirectionally. This provides a good alignment of the director along the electrodes and the bookshelf ... 

The picture predicted by Fig. 3.2 has been confirmed by birefiringence measurements on the isotropic phase [3, 7-10]. Such measurements are much more precise than attempts to measure the influence of an interface on the order parameter of the nematic phase, because there is no contribution to birefringence from the bulk of an isotropic liquid. For nematic layers with the director homogeneously oriented along the surface of a solid substrate rubbed unidirectionally, the birefiringence is observed at temperatures exceeding the N-I transition point. Moreover, it depends on the surface potential. Fig. 3.3, as predicted by theory [5]. The thickness of the quasi-nematic layers adjacent to the substrate can be calculated from the observed birefringence... 

Homogeneously planar oriented nematic elastomers have been prepared using a procedure very similar to that presented above. As alignment layers, unidirection-ally rubbed polyimide or rubbed poly(vinyl alcohol) were used [14]. 

A dye of negative dichroism can be mixed into a liquid crystal mixture of positive dielectric anisotropy and put in a cell having unidirectional homogeneous alignment [13-16,52,53]. A single polarizer is oriented in front of the layer, with its transmission axis parallel to the rubbing direction of the adjacent cell. The cell does not absorb in the quiescent state, as the transition moment of... 

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