title: Lehmann rotation of the cholesteric helix in droplets oriented by an electric field.
abstract: We study the Lehmann rotation of the cholesteric helix in droplets of the liquid crystal N-(p-methoxybenzilidene)-p-butylaniline doped with a small amount of the chiral molecule R811 when they are subjected to a temperature gradient. We show that the helix rotates much faster when it is parallel to the temperature gradient than when it is perpendicular to it. The first configuration is obtained by submitting the droplets to an ac electric field parallel to the temperature gradient, whereas the second one is observed at zero field. We show that the rotation velocity of the helix strongly depends on the droplet radius, even when the helix is parallel to the temperature gradient. This observation supports the idea that the Leslie thermomechanical coupling cannot explain alone the Lehmann effect.
authors.affiliation: Université de Lyon, Ecole Normale Supérieure de Lyon, Laboratoire de physique, 46 Allé d'Italie, 69364 Lyon, Cedex 07, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Oswald
authors.affiliation: Université de Lyon, Ecole Normale Supérieure de Lyon, Laboratoire de physique, 46 Allé d'Italie, 69364 Lyon, Cedex 07, France and Department of Applied Physics and Mathematics, University of Pardubice, 53210 Pardubice, Czech Republic.
authors.forename: Slavomir
authors.initials: S
authors.lastname: Pirkl
mesh_terms: D003198:Computer Simulation; D004574:Electromagnetic Fields; D050866:Liquid Crystals / Q000737:chemistry* / Q000528:radiation effects*; D008422:Materials Testing; D008956:Models, Chemical; D011829:Radiation Dosage; D012212:Rheology / Q000379:methods*; D012399:Rotation; D012996:Solutions; D013237:Stereoisomerism
chemical_list: D012996:Solutions