title: Bistable nematic and smectic anchoring in the liquid crystal octylcyanobiphenyl (8CB) adsorbed on a MoS2 single crystal.
abstract: We have studied the anchoring directions imposed on 4-n-octyl-4(')-cyanobiphenyl (8CB) smectic-A and nematic phases by a single crystal of molybdenum disulfide (MoS2). Combining optical microscopy and x-ray diffraction under grazing incidence we have demonstrated the occurrence of a bistable planar anchoring. A previous study of the two-dimensional (2D) network of adsorbed 8CB molecules under the liquid crystal film allows a direct connection to be made between the interface structure and the anchoring directions, demonstrating that bistability is induced by the presence of two dipolar groups in the skeleton of the 2D network. It is demonstrated that the Landau-de Gennes theory cannot account for the observed anchoring in the nematic phase. The Landau-de Gennes free energy has to be associated with a coupling with both the surface order and the MoS2 substrate to explain the experimental observations. The hypothesis of a nematic layer under the liquid crystal bulk is postulated in the smectic phase.
authors.affiliation: GPS, Universités Paris 6 et 7, UMR-CNRS 75-88, Campus Boucicaut, 140 rue de Lourmel, F-75015 Paris, France. lacaze@gps.jussieu.fr
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Lacaze
authors.forename: Jean Philippe
authors.initials: JP
authors.lastname: Michel
authors.forename: Michel
authors.initials: M
authors.lastname: Goldmann
authors.forename: Marc
authors.initials: M
authors.lastname: Gailhanou
authors.forename: Marc
authors.initials: M
authors.lastname: de Boissieu
authors.forename: Michel
authors.initials: M
authors.lastname: Alba