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Electric Birefringence of Liquid Crystalline Polymers
Published in Stoyl P. Stoylov, Maria V. Stoimenova, Molecular and Colloidal Electro-Optics, 2016
Igor’ P. Kolomiets, David Lacey, Peter N. Lavrenko
Macromolecules with laterally attached mesogenic side groups possess a unique ability to form thermotropic liquid crystals with a biaxial nematic phase [102] due to the hindered rotation of the side‐on‐fixed mesogens around their long axis. In spite of the claim that the fact of existence of this phase demands more confirmations [103], continuous attention was paid to these polymers [104–120] and the polymer‐based elastomers [113]. This type of attachment leads to a strong deformation of the undisturbed coil conformation and extension of the polymer chains parallel to the phase director results.
The formation of biaxial nematic phases in binary mixtures of thermotropic liquid-crystals composed of uniaxial molecules
Published in Molecular Physics, 2019
Robert A. Skutnik, Louis Lehmann, Sergej Püschel-Schlotthauer, George Jackson, Martin Schoen
Because of the alignment of the mesogens, nematic phases usually exhibit uniaxial symmetry. Biaxial nema-tic phases were first hypothesised by Freiser [7] in 1970. In a biaxial nematic phase, a second symmetry axis exists besides the nematic director. The existence of biaxial nematic phases remained controversial for many years at least as far as thermotropic liquid crystals are concerned. For example, in a review paper from 2001, Luckhurst [8] states that: ‘At present, then, thermotropic biaxial nematics would appear to be fiction but there is every expectation that they will become fact in the near future'. Three years later, Luckhurst [9] reached the conclusion that unambiguous evidence for the existence of a biaxial nematic phase was provided by NMR experiments carried out by Madsen et al. [10] (see also below). According to Luckhurst, NMR is best suited for the detection of biaxial nematic phases, whereas optical techniques are often misleading [9].