Metastable room-temperature twist-bend nematic phases via photopolymerization.

Abstract

The heliconical twist-bend nematic (N_{TB}) phase is a promising candidate for novel electro-optic and photonic applications. However, the phase generally exists at elevated temperatures and across a narrow temperature interval, limiting its implementation in device fabrication, which would ideally require the liquid crystal phase to be stable at room temperature. Here we report the formation of room-temperature N_{TB} phases by in situ photopolymerization. A complete phase diagram of the liquid crystal and monomer mixtures is presented and the nature of the polymerized samples is discussed in detail. In contrast to samples before polymerization-where the N_{TB} phases exist at elevated temperatures and across temperature intervals of width <10 °C-all photopolymerized N_{TB} samples are found to be stable at room temperature and exist over a temperature interval of up to 80 °C. Scanning electron microscopy of the polymerized N_{TB} phase shows that the polymer strands assemble at an angle with respect to the direction of the helical axis. This suggests that photopolymerized N_{TB} phases could be used to facilitate the tilt angle measurements in the twist-bend nematic phase.