Twist-bend nematics and heliconical cholesterics: a physico-chemical analysis of phase transitions and related specific properties

Certain nematic liquid crystals, e.g., those formed by banana-shaped molecules, can exhibit a low-temperature twist-bend (Ntb) phase. Upon addition of chiral dopants, version the phase (N*tb) be observed below conventional (N*) phase, while under electric field N* is transformed into specific state known as "heliconical cholesteric". In this work, we have studied well-known Ntb-forming system CB7CB:CB6OCB with 5CB and dopants (ChD) using optical microscopy, differential scanning calorimetry (DSC), measurements temperature-dependent transmission microscopy. Effects different (of steroid or non-steroid nature) upon thermal stability Ntb were analyzed, selective reflection in visible range could sufficiently high ChD content. As peculiar feature, sharp unwinding cholesteric helix was at lower temperatures when approaching N*tb which appears to similar close smectic-A transition.