Elastic properties of bimesogenic liquid crystals

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

“…29 As for the experimental determinations of the bend elastic constant over the uniform nematic phase of twist-bend liquid crystal dimers, it is observed that the bend elastic constant decreases as temperature decreases on approaching the N-N TB phase transition, leading to small values at the phase transition but increasing slightly or being nearly temperature independent before N TB is reached. 25,[30][31][32] In addition, very recently Yun et al 33 have tried to measure K 3 in the N TB phase of CB7CB showing anomalous and positive values.…”

Effect of cybotactic clusters on the elastic and flexoelectric properties of bent-core liquid crystals belonging to the same homologous series

“…They explained their observations by the molecular field theory and atomistic modeling, suggesting that K 11 is almost independent of the molecular conformation, whereas K 33 is sensitive to changes in the molecular curvature, similar to those calculated for odd-dimeric mesogens [35,44]. The elastic constants measured in some odd-dimeric compounds show similar trends as in BC systems, where K 33 < K 11 with K 33 decreasing steadily as temperature is reduced [35]. Our results for the three bent-core systems show that even in the absence of significant cybotactic clusters in C4, K 33 is lower than K 11 .…”

“…For C4 the The symbols with the bars denote the maximum possible errors present in the calculation due to the absence of a sharp threshold voltage V th and the errors involved in normalization of temperature between different setups used in finding different parameters for calculating K 11 and K 33 using the iterative procedure given in Ref. [35]. ratio only decreases from ∼0.85 to 0.78 as the temperature is lowered, while for C7 the ratio is also seen to vary slightly from ∼0.46 to 0.39 in the temperature range measured.…”

“…The optical retardation, δ, of a planarly aligned sample was measured as a function of the electric field for different temperatures using a photoelastic modulator (PEM) setup [35] and a polarizing microscope. A helium-neon laser is a source of monochromatic light to the PEM setup and the signal from the detector is amplitude and phase locked using two lock-in amplifiers.…”

“…The bend elastic constant, K 33 , was obtained from a theoretical fit of the retardation data for a planar cell, for voltages greater than the threshold voltage, to Eqs. (4) and (5) [36,37] using an iterative procedure designed by us [35],…”