Dresden 2006 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 6: Electronic Structure and Spectroscopy I
CPP 6.11: Talk
Monday, March 27, 2006, 17:15–17:30, ZEU 114
Thermodynamic theory of light-induced material transport in amorphous azobenzene polymer films — •Marina Saphiannikova1 and Dieter Neher2 — 1Leibniz Institute of Polymer Research, Hohe Str. 6, 01069 Dresden, Germany — 2Institute of Physics, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
It was discovered 10 years ago that the exposure of an initially flat layer of an azobenzene containing polymer to an inhomogeneous light pattern leads to the formation of surface relief structures, accompanied by a mass transport over several micrometers. However, the driving force of this process is still unclear.
We propose a new thermodynamic approach that explains a number of experimental findings including the light-induced deformation of free standing films and the formation of surface relief gratings for the main inscription geometries. Our basic assumption is that under homogeneous illumination an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film. Orientational distributions of chromophores predicted by our model are compared with those deduced from Raman intensity measurements.