0000000000637063
AUTHOR
Joachim Stumpe
Optical suppression of ferroelectricity in polysiloxane copolymers with chiral and photochromic side groups
The ferroelectricity of surface-stabilized aligned films of polysiloxane copolymers containing chiral esters and photochromic azobenzene moieties within the side groups is suppressed on UV irradiation and is rebuilt on visible irradiation. The liquid crystalline polymer (Sc* 64 SA 80 i) shows ferroelectric behavior below 64°C. The photoinduced modification of supramolecular order and the corresponding changes in its dynamics are studied by polarized UV/vis spectroscopy and broad band dielectric spectroscopy (10−2–105 Hz). The dielectric measurements show that UV irradiation causes a loss of ferroelectricity within an interval of 10 K below the phase transition temperature. The photochemical…
Light Induced Modifications of Langmuir-Blodgett-Multilayer Assemblies Containing Amphotropic Azocopolymer
Abstract Photochromic LB-multilayers of amphotropic copolymers having rod-like azobenzene moieties as side groups which exhibit thermotropic liquid crystalline behaviour in the bulk have been characterized by UV-VIS spectroscopy as well as by angular dependent and energy dispersive SAXS. Upon irradiation with UV-light the initial optical in-plane anisotropy and the vertical layered structure of LB-films can be destroyed. A new layered structure can be rebuilt on irradiation with visible light or by annealing. Using linearly polarized light for the irradiation an optical anisotropy (POA) has been induced or reversibly modified by a photoselection process.
Ordering and dewetting in spin-coated films of a liquid crystalline main chain polymer
Abstract The ordering of spin-coated films of a main-chain smectic liquid crystalline polymer with an azobenzene group connected by flexible spacers to a phenyl malonate unit has been studied as a function of film thickness using scanning force microscopy and UV/Vis spectroscopy. Already the as-prepared films are characterized by a significant out-of-plane orientation of the azobenzene groups. Annealing of films thicker than 7 nm results in aggregation and homeotropical alignment of azobenzene groups forming smectic layers parallel to the substrate. An optically isotropic mesophase was found upon annealing in the temperature range of smectic mesophase. Films thinner than the bilayer thickne…