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Neste trabalho foi feito o estudo do efeito de orientação de moléculas de cristal líquido (5CB) em superfícies recobertas com fotopolímeros. Estudamos o processo de alinhamento fotoinduzido às moléculas de cristal líquido, de forma a caracterizar a intensidade de energia de ancoramento em função da energia de luz incidente e da concentração de cromóforos nos fotopolímeros. Foi realizado um estudo do efeito de competição entre duas direções distintas induzidas por fotoalinhamento, através da gravação de microtexturas periódicas. Neste trabalho, foi utilizado um modelo teórico para explicar como se dá a transição orientacional conforme se muda o período da textura periódica gravada. Foi feito também a gravação de grades de relevo nesses materiais, utilizando luz polarizada com alta potência incidente através da técnica de interferência de luz. O objetivo principal deste trabalho seria uma tentativa de se realizar o efeito de competição de alinhamento entre os processos fotoinduzidos: um efeito de fotoalinhamento, levando em conta a orientação das cadeias poliméricas, e outro de relevo, levando em conta a deformação da superfície tratada. Um resultado obtido foi a impossibilidade de se realizar este estudo, pois as intensidades de energia de ancoramento induzidas envolvidas diferem entre si de um fator de duas ordens de grandeza, mostrando que a direção de fotoalinhamento sempre acaba prevalecendo. Para contornar este problema, foi estudada a competição de fotoalinhamento com a técnica de rubbing, tendo em vista que as intensidades de energia de ancoramento estudadas eram compatíveis entre si. / In this work we performed a study of the orientacional effect of the liquid crystals molecules in substrates coated with azopolymers films. We studied the photoalignment induced to liquid crystals molecules to determine the behavior of the magnitude of anchoring energy as a function of incident energy and azodyes concentration in the polymer. Then we performed a competition study of the competition of photoalignment effect by recording a microtexture pattern on the azopolymer surface, with two directions of alignment. In this work, we also introduced a theoretical model to explain the orientacional transitions observed as we changed the period of the patterned microtexture. Another technique utilized was the Surface Relief Grating recording, by using polarized light with enough power and creating an interference pattern in the azopolymer surface, we were able to create a topological structure in the surface. The main objective of this work was supposed to investigate the competition between these two photoinduced effects, when one is caused by a photoalignment of the polymer chains, and the other is due to topological issues. We concluded that it was not possible to have competition between these two effects, mainly because the magnitude of the anchoring energy induced by SRG was found to be a hundred times smaller than the photoinduced one. As an alternative to this approach, we studied, then, the competition between the rubbing process and the photoalignment effect, as the magnitude of these two effects was found to be compatible.

Neste trabalho foi feito o estudo do efeito de orientação de moléculas de cristal líquido (5CB) em superfícies recobertas com fotopolímeros. Estudamos o processo de alinhamento fotoinduzido às moléculas de cristal líquido, de forma a caracterizar a intensidade de energia de ancoramento em função da energia de luz incidente e da concentração de cromóforos nos fotopolímeros. Foi realizado um estudo do efeito de competição entre duas direções distintas induzidas por fotoalinhamento, através da gravação de microtexturas periódicas. Neste trabalho, foi utilizado um modelo teórico para explicar como se dá a transição orientacional conforme se muda o período da textura periódica gravada. Foi feito também a gravação de grades de relevo nesses materiais, utilizando luz polarizada com alta potência incidente através da técnica de interferência de luz. O objetivo principal deste trabalho seria uma tentativa de se realizar o efeito de competição de alinhamento entre os processos fotoinduzidos: um efeito de fotoalinhamento, levando em conta a orientação das cadeias poliméricas, e outro de relevo, levando em conta a deformação da superfície tratada. Um resultado obtido foi a impossibilidade de se realizar este estudo, pois as intensidades de energia de ancoramento induzidas envolvidas diferem entre si de um fator de duas ordens de grandeza, mostrando que a direção de fotoalinhamento sempre acaba prevalecendo. Para contornar este problema, foi estudada a competição de fotoalinhamento com a técnica de rubbing, tendo em vista que as intensidades de energia de ancoramento estudadas eram compatíveis entre si. / In this work we performed a study of the orientacional effect of the liquid crystals molecules in substrates coated with azopolymers films. We studied the photoalignment induced to liquid crystals molecules to determine the behavior of the magnitude of anchoring energy as a function of incident energy and azodyes concentration in the polymer. Then we performed a competition study of the competition of photoalignment effect by recording a microtexture pattern on the azopolymer surface, with two directions of alignment. In this work, we also introduced a theoretical model to explain the orientacional transitions observed as we changed the period of the patterned microtexture. Another technique utilized was the Surface Relief Grating recording, by using polarized light with enough power and creating an interference pattern in the azopolymer surface, we were able to create a topological structure in the surface. The main objective of this work was supposed to investigate the competition between these two photoinduced effects, when one is caused by a photoalignment of the polymer chains, and the other is due to topological issues. We concluded that it was not possible to have competition between these two effects, mainly because the magnitude of the anchoring energy induced by SRG was found to be a hundred times smaller than the photoinduced one. As an alternative to this approach, we studied, then, the competition between the rubbing process and the photoalignment effect, as the magnitude of these two effects was found to be compatible.

No description available.

This dissertation covers some important topics on the liquid crystal-substrate surface effects, including theoretical derivations and confirming experimental results. The research work is expected to make important impacts on liquid crystal device designs and to open new doors for further research along these topics. In this dissertation, a novel high-electric-field technique is developed to characterize the anchoring energy of vertically-aligned liquid crystal cells. Both theoretical analyses and confirming experimental results are presented. Vertically-aligned liquid crystal cells with buffed polyimide alignment layers are used to validate the measurement techniques. Based on the voltage-dependent transmittance of the liquid crystal cells, a linear fitting can be obtained, which leads to a precise determination of the anchoring energy. If some specific liquid crystal material parameters are known, then the traditional cell capacitance measurements can be avoided. Anchoring energy and cell gap effects on liquid crystal response time is theoretically analyzed and experimentally investigated. A novel theory on the liquid crystal dynamics is developed. In this part, two different theoretical approaches are discussed: one is surface dynamic equation method and the other is effective cell gap method. These two different approaches lead to consistent results, which are also confirmed by our experimental results. This work opens a new door for LCD industry to optimize liquid crystal response time, and it is especially critical for liquid crystal cells with thin cell gap, which is a promising approach for fast response time liquid crystal display. Pretilt angle effects on liquid crystal dynamics are analyzed theoretically and validated experimentally. Analytical expressions are derived to describe liquid crystal response time under nonzero pretilt angle conditions. The theoretical analysis is confirmed experimentally using vertically-aligned liquid crystal cells. These results quantitatively correlate pretilt angles with liquid crystal response time, which is important for optimizing liquid crystal response time.