title: Similarities and differences between molecular order in the nematic and twist-bend nematic phases of a symmetric liquid crystal dimer.
abstract: The order parameter, Szz, where z is the para axis of the difluoroterphenyl groups in DTC5C9, has been obtained from chemical shift anisotropies measured by (13)C - {(1)H} NMR experiments at temperatures throughout the nematic, NU, and twist-bend nematic, NTB, phases shown by this compound. The order parameter temperature profiles are unusual in having a maximum value in the NU phase and then decreasing until the NTB phase is reached. There is a small discontinuity (∼2%) in Szz at TNNTB and then a gradual decrease until a new phase appears. This behaviour is interpreted as revealing a temperature-dependent tilting of local directors in both phases away from the applied magnetic field direction. In the enantiomorphic twist-bend phase this tilt is consistent with the structure of the phase as a helical arrangement of local directors, whilst in the high-temperature non-chiral nematic the tilt must involve a non-chiral arrangement. It is proposed that in both phases the tilting of directors has a common origin in the bent shape of the molecules.
authors.affiliation: Department of Chemistry, University of Southampton, Southampton SO17 1BJ, UK. jwe@soton.ac.uk.
authors.forename: J W
authors.initials: JW
authors.lastname: Emsley
authors.affiliation: Institut des Sciences Analytiques, Centre RMN à Très Hauts Champs (CRMN), CNRS/ENS Lyon/UCB-Lyon 1, 5 rue de la Doua, 69100 Villeurbanne, France. moreno.lelli@ens-lyon.fr.
authors.forename: M
authors.initials: M
authors.lastname: Lelli
authors.affiliation: Department of Chemistry, University of Hull, Hull HU6 7RX, UK. G.H.Mehl@hull.ac.uk.
authors.forename: H
authors.initials: H
authors.lastname: Joy
authors.affiliation: Department of Chemistry, University of Hull, Hull HU6 7RX, UK. G.H.Mehl@hull.ac.uk.
authors.forename: M-G
authors.initials: MG
authors.lastname: Tamba
authors.affiliation: Department of Chemistry, University of Hull, Hull HU6 7RX, UK. G.H.Mehl@hull.ac.uk.
authors.forename: G H
authors.initials: GH
authors.lastname: Mehl