title: Solid-state 13C NMR study of cholesteric liquid crystals.
abstract: We investigated the structural behavior of cholesteric liquid crystals of 4-(hexyloxy)-4'-cyanobiphenyl (6OCB) in an 11.7 T magnetic field by solid-state (13)C nuclear magnetic resonance. Five 6OCB cholesteric liquid crystal systems were prepared with 4-methoxyphenyl 3,4-O-isopropylidene-2,6-bis-O-(4-methylbenzoyl)-β-d-galactopyranoside (CR), in which 6OCB was doped with 0.51, 1.00, 2.34, 5.60, and 6.47 mol % CR, giving products with helical twisting powers (HTPs) of 0.28, 0.54, 1.27, 3.05, and 3.52 μm(-1), respectively. Analyses of the alignment-induced shifts showed that the liquid crystals directors in pure 6OCB and 6OCB doped with 0.51 and 1.00 mol % CR become aligned with the 11.7 T magnetic field direction. However, 6OCB doped with 2.34, 5.60, and 6.47 mol % CR retained their cholesteric structures when the magnetic field was applied. The critical HTP value for resisting realignment by magnetic field was estimated to be approximately 1.27 μm(-1). A biaxiality of the phase was partially considered during spectral simulations, although the molecular shape of 6OCB can be defined as cylinderical when it is rotating rapidly. Our current understanding is that the order parameters in the cholesteric structures are not uniform; i.e., the molecular directors already aligned almost perpendicular to the magnetic field are significantly perturbed by the external field.
authors.affiliation: Department of Chemistry and Materials Science, and ‡Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology , O-okayama, Meguro-ku, Tokyo 152-8552, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Yamada
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Marumo
authors.forename: Sungmin
authors.initials: S
authors.lastname: Kang
authors.forename: Kenzo
authors.initials: K
authors.lastname: Deguchi
authors.forename: Toshihito
authors.initials: T
authors.lastname: Nakai
authors.forename: Tadashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Junji
authors.initials: J
authors.lastname: Watanabe