Polymerisation of twist-bend nematic textures for electro-optical applications

Abstract

Polymer-stabilised liquid crystals (PSLCs) have recently been used to maintain the focal conic domains (FCDs) typical of the smectic A phase in the nematic phase for smart window applications. The newly discovered twist-bend nematic phase of bent-shaped dimers also exhibits FCDs due to its pseudo-layered structure. The variety of topological defects in the N_TB phase is arguably even greater than in the smectic A phase, but the N_TB phase is often metastable and usually crystallises at room temperature, which hinders its use in electro-optical applications. Here we show how different textures (FCDs, rope-like texture, double helices) of the N_TB phase can be polymerised and then maintained in the nematic phase, at room temperature. This allows us to combine in PSLCs the optical properties of these defects, the thermal stability of the nematic phase and its reversible response to an electric field. We also show that the polymerised FCDs of the N_TB phase could be used in smart glass applications and that the polymerised rope-like texture could be of interest for optical modulators and beam steering. In addition, the polymerisation of double helices could help to better understand their formation and structure in the N_TB phase. More fundamentally, our work shows that despite the lack of density modulation, the textures of the N_TB phase, thanks to its periodic character, can be exploited in the same way as those of the smectic A phase.