• JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
  • JoomlaWorks Simple Image Rotator
 
  Bookmark and Share
 
 
Doctoral Thesis
DOI
10.11606/T.43.1991.tde-09122013-152726
Document
Author
Full name
Antonio Jose Palangana
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1991
Supervisor
Committee
Figueiredo Neto, Antonio Martins (President)
Amaral, Lia Queiroz do
Jayaraman, Subramania
Rechenberg, Hercilio Rodolfo
Santos, Marcus Bastos Lacerda
Title in Portuguese
Estudo da mesofase liotrópica na fase Nc submetida a campo magnético: determinação de K3 e X'alfa' e geração de instabilidades hidrodinâmicas.
Keywords in Portuguese
Cristais líquidos liotrópicos
Instabilidades térmicas
Matéria condensada
Medidas de constantes elásticas e anisotropia de susceptibilidade diamagnética
Abstract in Portuguese
No presente trabalho foram estudadas, inicialmente, distorções periódicas "bend" provocadas por campo magnético em amostra nemática calamítica da mistura: decilsulfato de sódio, decanol e água. Com base na teoria elástica continua, medidas do comprimento de onda das distorções periódicas permitiram obter a razão K IND. 9 / X IND. em função da temperatura, onde K IND. 9 é a constante elástica de "bend" e X IND. a anisotropia de susceptibilidade diamagnética. Em seguida, amostras nemáticas foram dopadas com ferrofluído em diferentes concentrações, o que possibilitou, através da comparação entre os resultados (com e sem o "doping"), determinar K IND. 9 e X IND. , respectivamente. Num segundo momento, a mesofase nemática calamítica obtida da mistura liotrópica de laurato de potássio, decanol e água, é submetida a gradiente térmico vertical em configuração planar. Uma nova instabilidade térmica foi observada envidenciando uma estrutura de rolos com os seus eixos perpendiculares à configuração inicial do diretor. O comprimento de onda da instabilidade tem valores em torno de 10 vezes menores que a espessura da amostra. A instabilidade, cujo processo de formação e relaxação é estudado, aparece com a diminuição do gradiente térmico próximo à transição de fase nemático-isotrópica. Considerando-se estes fatos, sugere-se um mecanismo em função da variação das dimensões dos objetos micelares com a temperatura.
Title in English
Study of lyotropic mesophase phase Nc subjected to magnetic field: determination of K3 and X and generation of hydrodynamic instabilities.
Keywords in English
Condensed matter
Lyotropic liquid crystals
Measurements of elastic constants and anisotropy of diamagnetic susceptibility
Thermal instabilities
Abstract in English
In this work were primarily studied the periodic distortions "bend" provoked by magnetic field on calamitic nematic sample of the mixture: sodium decylsulfate, decanol and water. Based on the continuum elastic theory, measures of the wave lenght of periodic distortions permitted to obtain the ratio K9 /X in function of the temperature, where k9 is the elastic constant of "bend" and x the anisotropic of diamagnetic susceptibility. Afterwards, nematic samples were doped with ferrofluid in different concentrations, which made possible, through a comparison between the results (with and without the "doping"), to determine x and K9 respectively. In a second moment, the calamitic nematic mesophase obtained from the liotropic mixture of potassium laurate, decanol and water is submitted to a vertical thermic gradient in plane configuration. A new thermic instability was observed showing evidences of a roll structure with its perpendicular axis to the initial configuration of the director. The lenght of the instability wave has values around ten times smaller than the thickness of the sample. The instability, whose process of formation with the decrease of the thermic gradient next to the transition of isotropic-nematic phase. Considering these facts, we would suggest a mechanism related to the variation of the micelar objects dimensions in function of the temperature.
 
WARNING - Viewing this document is conditioned on your acceptance of the following terms of use:
This document is only for private use for research and teaching activities. Reproduction for commercial use is forbidden. This rights cover the whole data about this document as well as its contents. Any uses or copies of this document in whole or in part must include the author's name.
45896Palangana.pdf (1.43 Mbytes)
Publishing Date
2014-02-21
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • KROIN, T., PALANGANA, A. J., and Neto, A.M.F. Determination of the bend elastic constant and the anisotropy of diamagnetic susceptibility of lyotropic nematic calamitic liquid crystals [doi:10.1103/PhysRevA.39.5373]. PHYS. REV. A [online], 1989, vol. 39, nº 10, p. 5373-5377.
  • PALANGANA, A. J., and Neto, A.M.F. Measurements of the ratio between the bend elastic constant and the anisotropy of diamagnetic susceptibility of a lyotropic nematic liquid crystal as a function of the temperature [doi:10.1103/PhysRevA.41.7053]. PHYSICAL REVIEW A [online], 1990, vol. 41, p. 7053-7055.
  • PALANGANA, A. J., DEPEYROT, J., and Neto, A.M.F. New Thermal Instability In A Lyotropic Uniaxial Nematic Liquid Crystal [doi:10.1103/PhysRevLett.65.2800]. PHYSICAL REVIEW LETTERS [online], 1990, vol. 65, p. 2800-2803.
All rights of the thesis/dissertation are from the authors
Centro de Informática de São Carlos
Digital Library of Theses and Dissertations of USP. Copyright © 2001-2020. All rights reserved.