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arXiv · 1511.07523

The twist-bend nematic phase of bent mesogenic dimer CB7CB and its mixtures

Michael R. Tuchband·Min Shuai·Keri A. Graber·Dong Chen·Leo Radzihovsky·Arthur Klittnick·Lee Foley·Alyssa Scarbrough·Jan H. Porada·Mark Moran·Eva Korblova·David M. Walba·Matthew A. Glaser·Joseph E. Maclennan·Noel A. Clark
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Abstract

Binary mixtures of the twist-bend nematic-forming liquid crystal CB7CB with the prototypical rod-like liquid crystal 5CB exhibit a twist-bend nematic phase with properties similar to those reported for neat CB7CB. The mixtures appear homogeneous, with no micron- or nano-scale segregation evident at any concentration. The linear dependence of the phase transition temperature on concentration indicates that these binary mixtures are nearly ideal. However, a decrease in the viscosity with the addition of 5CB allows the characteristic twist-bend stripe textures to relax into a state of uniform birefringence. We confirm the presence of nanoscale modulations of the molecular orientation in the mixtures by freeze-fracture transmission electron microscopy (FFTEM), further evidence of their twist-bend nature. We devise and implement a statistical approach to quantitatively measure the ground state pitch of the twist-bend phase and its mixtures using FFTEM. The addition of 5CB generally shifts the measured ground-state pitch distributions towards larger pitch. Interestingly, the pitch appears to increase discontinuously by ~10 nm at the 50 wt% concentration of 5CB, indicating that the twist-bend phase undergoes a structural transition at higher 5CB concentrations.

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Michael R. Tuchband, Min Shuai, Keri A. Graber, Dong Chen, Leo Radzihovsky, Arthur Klittnick, Lee Foley, Alyssa Scarbrough, Jan H. Porada, Mark Moran, Eva Korblova, David M. Walba, Matthew A. Glaser, Joseph E. Maclennan, Noel A. Clark. 2015-11-24. The twist-bend nematic phase of bent mesogenic dimer CB7CB and its mixtures. https://arxiv.org/abs/1511.07523

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