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Doctoral Thesis
DOI
10.11606/T.43.1996.tde-03122013-150921
Document
Author
Full name
Paulo Ricardo Garcia Fernandes
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1996
Supervisor
Committee
Figueiredo Neto, Antonio Martins (President)
Bittencourt, Diomar da Rocha Santos
Evangelista, Luiz Roberto
Figueiredo, Wagner
Tenan, Mário Alberto
Title in Portuguese
Birrefringência Induzida por Gradientes de Velocidades na Fase Isotrópica de um Cristal Líquido Liotrópico
Keywords in Portuguese
Cristais líquidos
Matéria condensada
Abstract in Portuguese
Na fase isotrópica de um cristal líquido liotrópico induziu-se uma birrefringência a partir de gradientes de velocidades. Os gradientes são produzidos pelo movimento de queda de uma placa plana no interior da amostra. O diagrama de fases (da mistura KL/DeOH/H2O) em função da temperatura apresenta duas fases lamelares (L) limitando a fase isotrópica(I). A perturbação mecânica introduzida na fase isotrópica da mistura induz uma birrefringência que relaxa com um tempo característico, , da ordem de 10 POT -2s. A birrefringência induzida por gradientes de velocidades na fase isotrópica é tratada como um processo de difusão de ordem no interior da mistura. Nesta proposição determina-se, experimentalmente, um comprimento característico, l (que informa sobre as propriedades de correlação entre as micelas), a partir de medidas de transmitância em função do tempo. Esse parâmetro é da ordem de 10 POT -5 cm. O comportamento de e l em função da temperatura indica a existência de uma fase nemática virtual (FNV) no domínio isotrópico.
Title in English
Birefringence induced velocity gradients in the isotropic phase of a lyotropic liquid crystal
Keywords in English
Condensed matter
Liquid crystals
Abstract in English
The flow birefringence induced in a lyotropic mixture in the isotropic phase was produced by means of velocities gradients. The gradients are produced by the movement of a plate inside the sample. As a function of temperature, the isotropic phase(I) is surrounded by two lamellar(L) phases in the phase diagram (mixture KL/DeOH/H2O). The shear flow produced by a perturbation in the isotropic phase induces a birefringence which relaxes with a typical relaxation time, ~10-2 s. The birefringence induced by velocities gradients is treated by means of an order diffusion process into the mixture. In this approach a characteristic length, l, (which informs about the correlation properties between the micelles) is experimentally obtained with the measurement of the transmittance as a function of the time. This parameter is about 10-5cm. The behavior of and 1: versus temperature indicate the existence of a virtual nematic phase(VNP) in the isotropic phase.
 
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Publishing Date
2014-02-18
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • FERNANDES, P. R. G., and Neto, A.M.F. Flow Birefringence In Lyotropic Mistures In The Isotropic Phase [doi:10.1103/PhysRevE.51.567]. PHYSICAL REVIEW E (STATISTICAL PHYSICS, PLASMAS, FLUIDS AND RELATED INTERDISCIPLINARY TOPICS) [online], 1995, vol. 51, p. 567-570.
  • FERNANDES, P. R. G., and Neto, A.M.F. Flow-induced birefringence in a lyotropic liquid crystal in the isotropic phase: An order diffusion approach [doi:10.1103/PhysRevE.56.6185]. Physical Review E [online], 1997, vol. 56, p. 6185-6188.
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