title: Light-induced pitch transitions in photosensitive cholesteric liquid crystals: effects of anchoring energy.
abstract: We experimentally study how the cholesteric pitch P depends on the equilibrium pitch P0 in planar liquid crystal (LC) cells with both strong and semistrong anchoring conditions. The cholesteric phase was induced by dissolution in the nematic LC of the right-handed chiral dopant 7-dehydrocholesterol (7-DHC, provitamin D3) which transforms to left-handed tachysterol under the action of uv irradiation at the wavelength of 254 nm. By using the model of photoreaction kinetics we obtain the dependencies of isomer concentrations and, therefore, of the equilibrium pitch on the uv irradiation dose. The cholesteric pitch was measured as a function of irradiation time using the polarimetry method. In this method, the pitch is estimated from the experimental data on the irradiation time dependence of the ellipticity of light transmitted through the LC cells. It is found that the resulting dependence of the twist parameter 2D/P (D is the cell thickness) on the free twisting number parameter 2D/P0 shows jumplike behavior and agrees well with the known theoretical results for the anchoring potential of Rapini-Papoular form.
authors.affiliation: Institute of Physics of National Academy of Sciences of Ukraine, Prospekt Nauki 46, 03680 Kiev, Ukraine and LOMA (Laboratoire Ondes et Matiere d'Aquitaine), University Bordeaux 1, 351 Cours de la Liberation, 33400 Talence, France.
authors.forename: Tetiana N
authors.initials: TN
authors.lastname: Orlova
authors.affiliation: Institute of Physics of National Academy of Sciences of Ukraine, Prospekt Nauki 46, 03680 Kiev, Ukraine and UFOLAB (Ultrafast Optics &amp; Lasers Laboratory), Bilkent University, 06800 Bilkent, Ankara, Turkey.
authors.forename: Roman I
authors.initials: RI
authors.lastname: Iegorov
authors.affiliation: Institute of Physics of National Academy of Sciences of Ukraine, Prospekt Nauki 46, 03680 Kiev, Ukraine.
authors.forename: Alexei D
authors.initials: AD
authors.lastname: Kiselev
mesh_terms: D003198:Computer Simulation; D004735:Energy Transfer / Q000528:radiation effects; D008027:Light; D050866:Liquid Crystals / Q000737:chemistry* / Q000528:radiation effects*; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D011829:Radiation Dosage; D012031:Refractometry / Q000379:methods*