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Doctoral Thesis
Full name
Teodosio Kroin
Knowledge Area
Date of Defense
São Paulo, 1990
Figueiredo Neto, Antonio Martins (President)
Oliveira, Mario Jose de
Santos, Marcus Bastos Lacerda
Taylor, Ted Ray
Vanin, Jose Atilio
Title in Portuguese
Distorção periódica tipo "bend" e estudo da biaxialidade induzida por um campo quiral em cristais líquidos liotrópicos
Keywords in Portuguese
Cristais líquidos
Materiais magnéticos
Abstract in Portuguese
A criacao de uma textura periodica por acao de um campo magnetico na fase nematica calamitica de um cristal liquido liotropico, usando a teoria elastica do continuo e estudada. O periodo (p) desta distorcao permite a obtencao da grandeza K IND.3/X IND.ALFA, onde K IND.3 e a constante elastica bend e X IND.ALFA e a anisotropia de susceptibilidade diamagnetica. A existencia de um campo magnetico critico de fredericskz, permite a determinacao de K IND.2/X IND.ALFA, onde K IND.2 e a constante elastica twist. Dopando a amostra com ferrofluido e comparando os resultados de medidas nestas amostras com medidas em amostras sem dopagem, determina-se o valor de X IND.ALFA. A biaxialidade induzida por um agente quiral e medida na transicao de fase colesterica uniaxial-colesterica biaxial no sistema liotropico: laurato de potassio, 1-decanol, agua e um dopante quiral. As medidas mostram que esta transicao e continua mas nao de segunda ordem, como ocorre na transicao nematica uniaxial-nematica biaxial. Esta mudanca e interpretada como um efeito do campo elastico quiral presente nas fases colestericas.
Title in English
Periodic bend distortion and study of induced biaxiality by a chiral field in lyotropic liquid crystals
Keywords in English
Liquid crystals
Magnetic materials
Abstract in English
The creation of periodic distortion by the action of a magnetic fields in a nematic calamitic lyotrop liquid crystal using the continuum elastic theory is discussed. The wavelength (P) of that distortion allows the measurement of k3/a, where k3 is the bend elastic constant and a the anisotropy of diamagnetic susceptibility. The existence of a Fredericskz critical magnetic field allows the measurement of k2/a, where k2 is the twist ferrofluid and comparing the measurements in this new sample with those in samples without doping the value of a is obtained. The chirality-induced biaxility is measured at the uniaxial to biaxial cholesteric phase transition of the lyotropic system: potassium laurate, 1-decanol, water and some chiral agent. The measurements show that the uniaxial to biaxial cholesteric phase transition is continuous but not second order as the uniaxial to biaxial nematic phase transition. This change is interpreted to be an effect of the chiral elastic field present in the cholesteric phases.
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  • KROIN, T., et al. Chirality Induced Biaxiality At The Uniaxial-To-Biaxial Cholesteric Phase Transition [doi:10.1103/PhysRevA.40.4647]. PHYS. REV. A [online], 1989, vol. 40, nº A, p. 4647-4651.
  • KROIN, T., and Neto, A.M.F. Bend Periodic Distortion Of The Texture In Nematic Lyotropic Liquid Crystals With And Without Ferrofluid [doi:10.1103/PhysRevA.36.2987]. PHYS. REV. A [online], 1987, vol. 36, nº 6, p. 2987-2990.
  • 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.
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