Direct Observation of Heliconical Pitch in the Twist-bend Nematic Liquid Crystal Phase of Bent Molecular Dimers

ORAL

Abstract

Nanometer-scale modulation of the director field is directly observed using freeze-fracture transmission electron microscopy (FFTEM) in the heliconical twist-bend nematic (N$_{\mathrm{TB}})$ phase, a periodic mesophase with no detectable modulation of the electron density [Chen, D., \textit{et al}., PNAS, 2013, 110(40):15931--15936]. A homologous series of achiral odd-methylene-linked~dimers CB$m$CB ($m =$ 5, 7, 9, and 11) and binary mixtures with simple cyanobiphenyl $n$CBs ($n =$ 5, 6, 7, and 8) in the N$_{\mathrm{TB}}$ phase has been studied. The helix pitch is found to vary between 6 and 11 nm. Increase the m or n value increases the helix pitch. Meanwhile, surprisingly, the helix pitch becomes shorter as the monomer concentration in the mixtures increases. FFTEM images show homogenous phases and preliminary measurements of the transition temperature versus concentration indicate that the binary mixtures are close to ideal. Polarized optical microscopy and calorimetry are carried out to study the nature of the N-N$_{\mathrm{TB}}$ transition in detail.

*This work is supported by NSF MRSEC Grant DMR-0820579, ICAM Postdoctoral Fellowship Award OCG5711B, and ED GAANN Award P200A120014.

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Authors

  • Min Shuai

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Michael Tuchband

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Dong Chen

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Arthur Klittnick

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Joseph Maclennan

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Matthew Glaser

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Noel Clark

    • Department of Physics and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • Eva Korblova

    • Department of Chemistry and Biochemistry and Liquid Crystal Materials Research Center, University of Colorado - Boulder

  • David Walba

    • Department of Chemistry and Biochemistry and Liquid Crystal Materials Research Center, University of Colorado - Boulder