Hierarchical elasticity of bimesogenic liquid crystals with twist-bend nematic phase

Abstract

Measurement of nematic liquid crystal splay elastic constants by disclination line motion in high pretilt, negative dielectric anisotropy pi-cells

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

“…Eqn (18a) defines an effective bend elastic constant (K eff 3 ) which is a function of temperature because K 3 varies with temperature for liquid crystal dimers, 29 but is definite positive in the uniform nematic phase according to experimental determinations, 25,[31][32][33][34]54 as shown in Fig. 4.…”

“…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 polar intermolecular interactions on the elastic constants of bent-core nematics and the origin of the twist-bend phase

“…It should be noted that the key assumption about the decrease of the bend elastic constant has been indeed confirmed experimentally [3,8,15]. Clearly it is impossible to measure negative elastic constants, but very low positive values of K 33 have been observed directly above the transition into the TB phase [3,8,15].…”

Twist-bend nematic phases of bent-shaped biaxial molecules

“…Before going further it seems appropriate to discuss similarities and differences between the present model (8) and that of GLF. To this end we rewrite the GLF Hamiltonian in our notation:…”

“…The director in N TB forms a conical helix with nanoscale periodicity, while molecular achirality implies that coexisting domains of opposite chirality are formed. Up to now, only some characteristic features of this elusive phase are known, like e.g., tilt angle and the pitch length or values of elastic constants in the vicinity of the uniaxial nematic (N U ) -N TB phase transition [8][9][10][11][12][13] . Experiments show that the N TB phase usually occurs within the stability regime of N U 14 , but for some compounds a direct transition between N TB and the isotropic phase (Iso) has also been found 15 .…”