Rubbing strength

Table 4.2. Comparison of anchoring energy coefficients of 4-n-pentyI-4 -cyanobiphenyl (5CB) at T = 32° C and 4-n-octyl-4-cyanobiphenyl (8CB) at T = 37° C on rubbed Nylon and photosensitive poly-(vinyl)-cinnamate. Different anchoring coefficients on rubbed Nylon are achieved by different rubbing strengths.

Fig. 2.10 Relation between the inclination angle of the polymer and the LC pretilt angle as a function of rubbing strength. Permission to print from [32], courtesy Society for Information Display.

To describe the rubbing strength quantitatively, a definition of rubbing strength is required. The structure of a rubbing machine is shown as Fig. 2.20. It consists of a rotating drum covered by a cloth whose surface is made of short fibres, and... 

Aerie etal. defined the rubbing strength as the rubbing density described as [22],... 

Fig. 2.22 Relation between the largest cell-gap to give homogeneous alignment, dai and the rubbing strength parameter, L, when n and N are changed independently. Reproduction by permission from [11].

Here, N, C, lo, and v are the number of times a location is rubbed, the diameter of the cylinder, the rotational speed of the cylinder, and the movement speed of the substrate stage, respectively. This equation is almost the same as Uchida s except that it does not include the contact length 1. Since the rubbing pressure is constant, the rubbing density does not include this parameter. In these equations, the rubbing strength is proportional to the number of times a substrate is rubbed. 

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.

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