title: Mesomorphism in columnar phases studied by solid-state nuclear magnetic resonance.
abstract: In this paper, we present 13C and 1H NMR investigations of 2, 3, 6, 7, 10, 11-hexahexyl-thiotriphenylene (HHTT). The measurements were carried out under both static and magic-angle spinning conditions. The phase diagram of HHTT is K<-->H<-->D(hd)<-->I , where H is a helical phase and D(hd) is a columnar liquid crystal. The motivation was to characterize the molecular order and dynamics and to investigate differences at the molecular level between the two mesophases: H and D(hd). It is shown that D(hd) is a conventional columnar liquid crystal, where the molecular core undergoes fast rotation about the symmetry axis. The orientational order in this mesophase is lower and the temperature dependence of the order parameter is steeper than in other triphenylene-based compounds. On the other hand, in the helical phase the core, similarly to the solid phase, is essentially rigid. The difference between the solid and helical phases is mainly manifested in an increased mobility of the aliphatic chains observed in the latter phase. In addition, the sample exhibits thermal history effects, which are observed in the different behavior upon cooling and heating.
authors.affiliation: Institute of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Dvinskikh
authors.forename: Johan
authors.initials: J
authors.lastname: Thaning
authors.forename: Baltzar
authors.initials: B
authors.lastname: Stevensson
authors.forename: Kjell
authors.initials: K
authors.lastname: Jansson
authors.forename: Sandeep
authors.initials: S
authors.lastname: Kumar
authors.forename: Herbert
authors.initials: H
authors.lastname: Zimmermann
authors.forename: Arnold
authors.initials: A
authors.lastname: Maliniak