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Master's Dissertation
DOI
https://doi.org/10.11606/D.43.2000.tde-02072004-141353
Document
Author
Full name
Ivan Helmuth Bechtold
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2000
Supervisor
Committee
Oliveira, Elisabeth Andreoli de (President)
Evangelista, Luiz Roberto
Fantini, Marcia Carvalho de Abreu
Title in Portuguese
Efeitos de Superfícies de Contorno na Orientação de Cristais Líquidos Liotrópicos
Keywords in Portuguese
Ancoramento
Cristais Líquidos Liotrópicos
Polímeros
Tratamento de Superfície
Abstract in Portuguese
Para uso em aplicações tecnológicas os cristais líquidos são geralmente confinados em em celas, onde a interação do cristal líquido com a superfície de contorno é de grande importância para o bom desempenho do dispositivo. Os cristais líquidos liotrópicos em particular, possuem propriedades físicas muito mais complexas que os termotrópicos, que não são conhecidas em sua totalidade. Dessa forma, desenvolvemos um estudo com o objetivo de investigar a influência da superfície na configuração de uma amostra de cristal líquido liotrópico. Utilizamos alguns tratamentos de superfície para alterar as condições de contorno e investigar a orientação induzida ao cristal líquido. Esses tratamentos alteram as propriedades físico-químicas das superfícies, tais como o caráter hidrofílico (utilizando lâminas de vidro) e hidrofóbico (utilizando lâminas de vidro recobertas com polímero). Outro tratamento empregado consiste no esfregamento dos substratos ao longo de uma direção preferencial que pode alterar a topografia das superfícies. Variamos a espessura da amostra para comparar os efeitos devido as interações da superfície em relação as interações entre as moléculas no volume. Efetuamos análise de textura da amostra de cristal líquido liotrópico após colocada nas celas fabricadas com os substratos tratados. Através de medidas de transmitância de um feixe de luz polarizada pela amostra, investigamos os processos dinâmicos de reorientação e relaxação induzidos por um campo magnético externo.
Title in English
Boundary Surface Effects on the Liotropic Liquid Crystal Orientation
Keywords in English
Anchoring
Liotropic Liquid Crystal
Polymers
Surface Treatment
Abstract in English
The use of liquid crystals (LC) in technological applications (LC displays) implies that these materials might be confined in thin cells, where the interactions with the boundary surfaces are of great importance for a good performance of such displays. The physical properties of lyotropic liquid crystals, in particular, are much more complexe than those of thermotropic LC, and are not up to now completely understood. Therefore, we have performed a study with the objective of investigating the influence of the boundary surface on the configuration of a lyotropic liquid crystal sample. Different surface treatments were used to modify the boundary conditions and to investigate the orientation induced to the liquid crystal. These surface treatments may affect the physico-chemical properties of the surfaces, such as the hydrophilicity (using clean glass plates) and hydrophobicity (by coating the glass plates with a polymer). Another treatment that have been used is the unidirectional rubbing of the substrates that can change the surfaces topography. The sample thickness was also varied in order to compare the effects due to surface interactions with respect to the intermolecular interactions in the bulk. We have performed an analysis of the texture of the lyotropic liquid crystal sample once confined in the cells built from the treated substrates. By means of the measurements of the intensity of a polarized light beam crossing the sample, we have investigated the dynamics of the reorientation and relaxation processes induced by the an external magnetic field.
 
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Publishing Date
2004-07-13
 
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