Rubbed surface observations measurements

To observe chemical changes in the rubbed surface, Lee and Paek measured the polarity of a rubbed surface by using water contact angle measurements, and discussed a correlation between the pretilt angle and the polarity of the rubbed surface [44,62]. The measurement method is illustrated in Fig. 2.2. 

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... 

To avoid the formation of surface walls and to provide a fast switching ofF time, the anchoring energy should be sufficiently high, e.g. > 10 " J/m, comparable with that of the rubbed polymer surface. This is not really observed for polyvinyl-cinnamate (PVCN) derivatives [27-29]. The recent measurements also confirm that 10 to 10 J/m, i.e. about one to two orders of mapitude smaller than the required value [1]. The in-plane sliding mode (IPSL) was proposed in a... 

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