title: Distinguishing the parallel and vertical orientations and optic axis characteristics determination of azobenzene mesogen by conoscopic polarized microscopy.
abstract: Orientational behaviours under the action of linearly polarized light and circularly polarized light of a side-chain azobenzene containing polymer were studied by conoscopic polarized microscopy. The results suggest that the linearly polarized light (473 nm, 20 mW cm(-2)) results in an in-plane orientation of the azobenzene groups. The irradiation with circularly polarized light (473 nm, 20 mW cm(-2)) leads to a tilt orientation (out-of-plane) of the azobenzene groups with the long axis of mesogens aligned along the propagation direction of the actinic light. Characteristic features of the in-plane and out-of-plane orientated films were obtained from their interference figures. The in-plane orientated film shows an interference cross consisting of a broad fuzzy bar, and the cross-centre lies in the centre of view field. In-plane orientated film also yields a flash figure upon a less than 10° rotation of the sample under polarized microscopy. The interference figures yielded from the out-of-plane orientated films consist of narrow bar cross. The locations of those interference figures depend on the oblique angle of the irradiation light. A method for distinguishing the in-plane orientation of the mesogens from the vertically out-of-plane orientation is demonstrated, which is based on comparing the bar width of their interference figures, and by whether they can produce a flash figure upon a small angle rotation of the film. The liquid crystalline film is identified as positive and uniaxial anisotropy after annealing of the perpendicularly irradiated film.
authors.affiliation: State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang, China. jianliu@swust.edu.cn
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Wang
authors.forename: M
authors.initials: M
authors.lastname: Dong
authors.forename: L
authors.initials: L
authors.lastname: Gao
authors.forename: J
authors.initials: J
authors.lastname: Tian