Eur. Phys. J. E 6, 57-67 (2001)
Spatial reorientation of azobenzene side groups of a liquid crystalline polymer induced by linearly polarized light
O. Yaroshchuk1, A.D. Kiselev2, Yu. Zakrevskyy1, J. Stumpe3 and J. Lindau41 Institute of Physics of NASU, pr. Nauki 46, 03028 Kyïv, Ukraine
2 Chernihiv State Technological University, Shevchenko Street 95, 14027 Chernihiv, Ukraine
3 Fraunhofer Institute of Applied Polymer Research, Erieseering 42, 10319 Berlin, Germany
4 Institute of Physical Chemistry, Martin-Luther University, Mühlphorte 1, 06106 Halle, Germany
kisel@elit.chernigov.ua
(Received 23 April 2001 and Received in final form 1 August 2001)
Abstract
The photoinduced 3D orientational structures in films of a
liquid crystalline polyester, containing azobenzene side groups,
are studied both experimentally and theoretically.
By using the null ellipsometry and the UV/Vis absorption spectroscopy,
the preferential in-plane alignment of the azobenzene
fragments and in-plane reorientation under irradiation with linearly polarized
UV light are established.
The uniaxial and biaxial orientational order of the azobenzene
chromophores are detected.
The biaxiality is observed in the
intermediate stages of irradiation, whereas the uniaxial structure is
maintained in the photosaturated state of the photo-orientation process.
The components of the order parameter
tensor of the azobenzene fragments are estimated for the initial state and
after different doses of irradiation.
The proposed theory takes into
account biaxiality of the induced structures.
Numerical analysis of the master equations for the order parameter tensor
is found to yield the results that are in good agreement with
the experimental dependencies of the order parameter components on the
illumination time.
61.30.Gd - Orientational order of liquid crystals; electric and magnetic field effects on order.
78.66.Qn - Polymers; organic compounds.
42.70.Gi - Light-sensitive materials.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
