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Colloidal Dispersions Lyotropic Liquid Crystals

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Author(s):
Viviane Moraes Alves
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
Defense date:
Examining board members:
Elisabeth Andreoli de Oliveira; Carlos Eugenio Imbassahy Carneiro; Marcia Carvalho de Abreu Fantini; Carlos Frederico de Oliveira Graeff; Manuel Simões Filho
Advisor: Elisabeth Andreoli de Oliveira
Abstract

In this work, the behavior of colloidal particles dispersed into a nematic lyotropic liquid crystal matrix is investigated. In such systems, there is a long range orientational order of the micelles in the volume. The micelles anchoring on the particles surfaces can be strong or weak, depending of the anchoring strength W, the particles radius R and the liquid crystal elastic constant K. For weak anchoring, the symmetry of the orientational order in the surroundings of the particles surfaces, and also in the volume, remains the same for both calamitic (\'N IND. c\') and discotic (\'N IND. d\') nematic phases. It was observed that high concentrated solution of nanometric silica particles in a lyotropic medium leads to phase segregation. In more diluted systems, the silica particles tend to organize themselves in the nematic medium for temperatures close to \'N IND. d\'. For 90nm latex particles in the lyotropic matrix, 3D anisotropic aggregates was observed in \'N IND. c\' phases. Although it was never observed before, this behavior was theoretically previewed. On the other hand, there are no aggregates in \'N IND. d\' phase. The different behaviors observed on \'N IND. c\' and \'N IND. d\' phases are related to the liquid crystalline medium organization, as well as to the interparticles and medium with particles interactions. It is also shown in this work, by direct measurements in a pure lyotropic liquid crystal confined between two surfaces, that the force profiles in function of the distance between surfaces are different for \'N IND. c\' and \'N IND. d\' phases. (AU)