Dielectric and viscoelastic investigations in a binary system of soft- and rigid-bent mesogens exhibiting the twist-bend nematic phase

We describe the dielectric and viscoelastic behaviour of a binary system consisting of rigid core and soft-bent nematogens, with the latter exhibiting in addition to the conventional nematic (N), the twist-bend nematic (NTB) phase. The propensity of bent architecture towards the twist-bend structures is evident from the fact that NTB phase gets induced by the addition of even a small amount of the soft-bent material, and exists over a large range of concentration. The salient features of the study include stronger antiparallel coupling, trend reversal in the thermal variation of the permittivity and its average value, observation of two relaxation processes corresponding to the director and cluster modes, significantly concentration-dependent splay and bend elastic constants along with drastic lowering of the elastic anisotropy. Thermal variation of rotational viscosity associated with the Freedericksz transformation for the different mixtures are also presented. These observations are explained using conformational changes of the individual molecules and cluster formations unique to bent structures exhibiting liquid crystallinity.