Indication of a Twist-Grain-Boundary-Twist-Bend Phase of flexible bent-shape chiral dimers.*

Flexible bent-core oligomers with odd-numbered methylene spacers exhibit a “twist-bend” nematic (N_TB) phase characterized by a nanoscale heliconical pitch. We designed mixtures of achiral dimers, which exhibit the N_TB phase, with a chiral additive. By differential scanning calorimetry, resonant soft X-ray scattering, polarized optical microscopy, and induced circular dichroism studies on condensed phases of these mixtures, we find, while in the nematic phase the micron-scale pitch of the additive-induced helical structure decreases with increasing additive concentration, in the N phase both the micron-scale and the nanoscale pitch of the ambidextrous spontaneous heliconical structure increase. At chiral additive concentrations above ~2% by weight, a new phase appears between the N* and N_TB* phases, which we propose to be analogous to the twist-grain-boundary (TGB) phase of chiral smectics; we designate this new phase by TGB_TB.