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| Author(s): |
Ivan Helmuth Bechtold
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. , gráficos, ilustrações, tabelas. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física (IF/SBI) |
| Defense date: | 2004-06-28 |
| Examining board members: |
Elisabeth Andreoli de Oliveira;
Wagner Figueiredo;
José Alberto Giacometti;
Rosangela Itri;
Antonio Domingues dos Santos
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| Advisor: | Elisabeth Andreoli de Oliveira |
| Field of knowledge: | Physical Sciences and Mathematics - Physics |
| Indexed in: | Banco de Dados Bibliográficos da USP-DEDALUS; Biblioteca Digital de Teses e Dissertações - USP |
| Location: | Universidade de São Paulo. Biblioteca do Instituto de Física; IF/TIFUSP; B392e D |
| Abstract | |
In this work we investigated the boundary surface and confinement effects on the orientational order of liquid crystals, where we used thermotropic and lyotropic liquid crystals. The importance of these studies refers to technological and fundamental research aspects. Regarding to the thermotropic liquid crystals, we determined that the electrostatic charges induced by rubbing of polymeric surfaces influence the liquid crystal orientational properties, these charges were measured with the electrostatic force microscopy technique (EFM). We studied new liquid crystal aligning forms with photosensitive polymers, where it was possible to impose a competition between two surface aligning potentials (surface relief gratings and photoalingment) and we created microtextured patterns of diferent alignment directions, which favors the use in bistable devices. In both cases, a local treatment can be achieved with a scaning near-field optical microscope (SNOM). With a surfactant (OTE) we produced periodic patterns of homeotropic and planar states to investigate the possibility of new orientational states induced to the liquid crystal, which are expected theoretically. The topographic analysis were done by atomic force microscopy (AFM) measurements and the liquid crystal texture was investigated with a polarized microscope. The confinement effect on a lyotropic liquid cristal was investigated according to theoretical approches of the dynamical behavior induced by external magnetic fields, giving evidences of a phase transition induced only due to the sample confinement. This phase transition was confirmed with direct measurements of the transition by using nonlinear optical techniques, as second harmonic generation and Z-scan. (AU) | |