title: Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) and comparison with CB7CB.
abstract: The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic-isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), (2)H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Building, Aberdeen, AB24 3UE, UK. c.t.imrie@abdn.ac.uk.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Paterson
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Gao
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA.
authors.forename: Young-Ki
authors.initials: YK
authors.lastname: Kim
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA.
authors.forename: Afsoon
authors.initials: A
authors.lastname: Jamali
authors.affiliation: Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain.
authors.forename: Kirsten L
authors.initials: KL
authors.lastname: Finley
authors.affiliation: Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Robles-Hernández
authors.affiliation: Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Diez-Berart
authors.affiliation: Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain.
authors.forename: Josep
authors.initials: J
authors.lastname: Salud
authors.affiliation: Department of Applied Physics II, University of the Basque Country, E-48080 Bilbao, Spain.
authors.forename: M Rosario
authors.initials: MR
authors.lastname: de la Fuente
authors.affiliation: Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
authors.forename: Bakir A
authors.initials: BA
authors.lastname: Timimi
authors.affiliation: Max-Planck-Institut für Medizinische Förschung, D-69120 Heidelberg, Germany.
authors.forename: Herbert
authors.initials: H
authors.lastname: Zimmermann
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35121 Padova, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Greco
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35121 Padova, Italy.
authors.forename: Alberta
authors.initials: A
authors.lastname: Ferrarini
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Building, Aberdeen, AB24 3UE, UK. c.t.imrie@abdn.ac.uk.
authors.forename: John M D
authors.initials: JM
authors.lastname: Storey
authors.affiliation: Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain.
authors.forename: David O
authors.initials: DO
authors.lastname: López
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA.
authors.forename: Oleg D
authors.initials: OD
authors.lastname: Lavrentovich
authors.affiliation: Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
authors.forename: Geoffrey R
authors.initials: GR
authors.lastname: Luckhurst
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Building, Aberdeen, AB24 3UE, UK. c.t.imrie@abdn.ac.uk.
authors.forename: Corrie T
authors.initials: CT
authors.lastname: Imrie