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Doctoral Thesis
DOI
10.11606/T.43.2000.tde-02122013-183735
Document
Author
Full name
Odair Gimenes Martins
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2000
Supervisor
Committee
Figueiredo Neto, Antonio Martins (President)
Giacometti, José Alberto
Guimarães Filho, Alberto Passos
Mesquita, Oscar Nassif de
Oliveira, Mario Jose de
Title in Portuguese
Método da Análise Espectral para a Deteminação da Polarização Dielétrica Espontânea, Aplicado a Cristais Líquidos Ferroelétricos
Keywords in Portuguese
Cristais líquidos
Dielétricos
Abstract in Portuguese
Um novo método de medida (SAM -Spectral Analysis Method) mostra que, devído a um erro sistemático tradicionalmente desprezado, os valores medidos de polarização espontânea do cristal líquido ZLI-3654 (Merck) não seguem o que é previsto pela teoria de Landau das transições contínuas. Porém, a variação da susceptibilidade elétrica relativa com a temperatura proporcional à (T Tc) IND.-1, onde Te é a temperatura onde ocorre o máximo da susceptibilidade ...... está de acordo com o modelo de Landau. A resposta em freqüência da constante dielétrica mostra que, a fim de minimizar a corrente iônica, as medidas de polarização elétrica devem ser realizadas em frequências acima de 20 Hz. Por sua vez, os valores dos ângulos de fase dos harmônicos da polarização, obtidos pelo novo método, indicam que a intensidade do campo elétrico aplicado deve ser inferior a 1, 1 x 10 IND.6 Vrms/m (em 23Hz) para que não ocorram instabilidades elctrohidrodinâmicas, Finalmente, o ajuste das amplitudes dos harmônicos da polarização elétrica obtidos pelo SAM aos parâmetros da equação de Landau-Kalatnikov mostra um bom acordo dos valores medidos com o modelo, em contraste com os valores de polarização espontânea, A solução da equação de equilíbrio, levando em consideração os parâmetros ajustados, mostra como seriam os valores da polarização espontânea sem os erros sistemáticos.
Title in English
Method of spectral analysis for determination of spontaneous dielectric polarization applied to ferroelectric liquid crystals.
Keywords in English
Dielectric
Liquid crystals
Abstract in English
A new proposed measurement method (SAM - Spectral Analysis Method) shows that, due a traditionally neglected systematic error, the values of the measured spontaneous polarization cf the ferroeleotric liquid crystal ZLI-3654 (Merck) doesn't follow what is predicted by the Landau theory of continuous transition. In contrast, the decay of the relative electric susceptibility with the temperature (T) - proportional to (T Tc)-l, where Tc is at the maximum of the susceptibility - is in good agreement with the Landau model. The frequency response of the dielectric constant shows that the measurements of the electric polarization of the sample must be done at frequencies hígher than 20Hz to avoid the actíons of the ionic currents. The phase values of the electric polarization harmonics obtained by the SAM indicates that the electric field must be lower thau 1,1 x l06Vrms/m (at 23Hz) to avoid electrohydrodynamic instabilities, Finally, the fitting of the amplitudes of the electric polarization harmonics obtained by the SAM to the parameters of the Landau-Kalatnikov equation shows a good agreement with the model, in contrast with the spontaneous polarization measurements. The solution of the Landau model, considering the fitted parameters, predicts how should be the spontaneous polarization values without the systematic errors.
 
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Publishing Date
2014-02-20
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • BARBERO, G., et al. Electrical response of a liquid crystal cell: The role of Debye's layer [doi:10.1063/1.2357554]. Applied Physics Letters [online], 2006, vol. 89, p. 132901.
  • BARBERO, G., et al. Ionic relaxation in nematic liquid crystal cells [doi:10.1080/02678290601097219]. Liquid Crystals [online], 2007, vol. 34, p. 343-348.
  • BATALIOTO, F., et al. The influence of adsorption phenomena on the impedance spectroscopy of an electrolytic cell [doi:10.1140/epje/i2011-11010-3]. The European Physical Journal. E, Soft Matter [online], 2011, vol. 34, p. 10.
  • F. R. Arantes, FIGUEIREDO NETO, Antônio Martins, e CORNEJO, D. R. Magnetic behavior of 10 nm-magnetite particles diluted in lyotropic liquid crystals [doi:10.1063/1.3549616]. Journal of Applied Physics [online], 2011, vol. 07E315, p. 109-111.
  • HUANG, M. Y. M., et al. Nanophase Segregation of Nonpolar Solvents in Smectic Liquid Crystals of Bent-Shape Molecules [doi:10.1103/PhysRevE.66.031708]. Physical Review E. (Cessou em 2000. Cont. 1539-3755 Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics) [online], 2002, vol. 66, p. 61.
  • Martins, Celma M, et al. Common sources and composition of phytosterols and their estimated intake by the population in the city of São Paulo, Brazil [doi:10.1016/j.nut.2012.12.017]. Nutrition (Burbank, Los Angeles County, Calif.) [online], 2013, vol. 29, p. 865-871.
  • MARTINS, O. G., et al. Electric field dependence of the electric conductivity in liquid crystals made of bent-core molecules [doi:10.1063/1.2206684]. Applied Physics Letters [online], 2006, vol. 88, p. 212904/ 1-212904/ 3.
  • TOLÉDANO, P., O. Gimenes Martins, and Neto, A.M.F. Coupling between tilt and polar orders in liquid crystal phases formed from achiral bent shaped molecules [doi:10.1103/PhysRevE.62.5143]. Physical Review E. (Cessou em 2000. Cont. 1539-3755 Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics) [online], 2000, vol. 62, p. 5143-5153.
  • MARTINS, O. G., et al. Lyo-banana mesophases composed by mixture of apolar solvents and bent-shapped molecules. In 5th Ibero - American Workshop on Complex Fluids and Their Applications, Maringá, 2001. Abstracts Maringá : Sociedade Ibero-Americana de Cristais Líquidos, 2001., 2001. Abstract.
  • Neto, A.M.F., et al. Effect of large electric field on the electrical conductivity of banana-like molecule (B-14) in the isotropic phase. In 21st International Liquid Crystal Conference - ILCC, Keystone, 2006. Abstracs Boulder : The Liquid Crystal Materials Research, 2006.., 2006. Abstract.
  • PEDREIRA, A. M., et al. Nano-phase segregation of non-polar solvents in smectic liquid crystals of bent-shape molecules. In XXV Encontro Nacional de Física da Matéria Condensada, Caxambu, 2002. Resumos São Paulo, 2002., 2002. Abstract.
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