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Mémoire de Maîtrise
DOI
10.11606/D.43.1994.tde-05082013-143439
Document
Auteur
Nom complet
Cilâine Verônica Teixeira
Adresse Mail
Unité de l'USP
Domain de Connaissance
Date de Soutenance
Editeur
São Paulo, 1994
Directeur
Jury
Itri, Rosangela (Président)
Henriques, Vera Bohomoletz
Torriani, Iris C Linares de
Titre en portugais
Estudo de fases isotrópicas e nemáticas líquido-cristalinas por espalhamento de raios-x a baixos ângulos
Mots-clés en portugais
Física do estado sólido
Matéria condensada
Resumé en portugais
Foram estudadas fases isotrópicas binárias concentradas de SLS/água próximo à transição isotrópica (I) hexagonal (H), e amostras ternárias de SLS/água/decanol, desde a fase isotrópica, abordando a transição I nemática (Nc) e todo o domínio Nc, até a transição Nc nemática discótica (Nd). A análise foi feita através da modelagem da intensidade espalhada, I(q), expressa como um produto do fator de forma, P(q), pela função de interferência entre partículas, S(q). No estudo das fases isotrópicas a função S(q) foi calculada via interações Coulombianas repulsivas "blindadas" em uma aproximação de esfera média (MSA), e o fator de forma P(q) foi calculado para micelas em forma de elipsóides prolatos e cilindros, comparando-se os dois resultados. Nas fases nemáticas modelou-se o fator de forma para cilindros paralelos perfeitamente orientados. A função de interferência foi calculada através do método MSA e os resultados obtidos foram comparados com os obtidos através de um outro método, que utiliza a função distribuição radial g(r) de uma fase isotrópica para o cálculo de S(q) de micelas cilíndricas orientadas. Os resultados indicam que pode haver crescimento das micelas na fase isotrópica binária, sendo o ajuste de cilindros mais adequado do que o de elipsóides prolatos, fato esse que concorda com estudos teóricos sobre a estabilidade dos agregados em função de sua energia de curvatura.
Titre en anglais
Study of isotropic and liquid-crystalline nematic phases with scattering of small angle X-ray
Mots-clés en anglais
Condensed matter
Physics of the solid state
Resumé en anglais
We have studied concentrated isotropic binary phases of SLS/water, near the isotropic (I) hexagonal (H transition, and ternary samples of SLS/water/decanol, from the isotropic to nematic phase, emphasizing the I nematic cilindric (Nc) transition, the whole Nc domain to the extent of Nc nematic discotic (Nd) transition. The analysis was done by modeling the scattered intensity, I(q), expressed as the product of the form factor, P(q), for the interference function among the particles, S(q). In the isotropic phases the S(q) function was chosen considering "screened" Coulombic repulsions in a Mean Spherical Approximation (MSA), and the form factor was calculated for prolate ellipsoids and cylinders. We thus compared both results. In the nematic phases we modeled the form factor considering parallel and perfect ordered cylinders. The interference function was calculated through the MSA method and the results were compared with others obtained through another method which uses the radial distribution function g(r) of an isotropic phase to calculate S(q ) for oriented cylindrical micelles. The results indicate that the micelles can grow in the isotropic binary phase and that the cylindrical shape is more adequate than the ellipsoidal one. This fact is in accordance with theoretical studies on the aggregates stability as a function of their bending energy. In theisotropic ternary phases we have observed the micellar growth until the I Nc transition is nearly totally achieved. In such region, however, the cylindrical shape is no longer as suitable. A deformation might probably be occuring in the micelle's transversal section as decanol has been added to the system. In the nematic domain there seems to have been occured no growing, but only a great deformation of the transversal section, where the micelles tend to take the discotic shape, until the Nc Nd transition. The values of anisometry obtained through the MSA method are in accordance with the experimental results obtained through NMR recently. Our results conform with the theoretical results which predict the I Nc Nd transitions, depending upon the self-aggregation process where the competition between the growth in the longitudinal and transversal directions take place.
 
Date de Publication
2013-08-06
 
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