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CPP: Chemische Physik und Polymerphysik

CPP 11: Light induced phenomena II

CPP 11.2: Vortrag

Montag, 7. März 2005, 11:30–11:45, TU C230

Light-induced mechanical and dielectrical changes in azobenzene polymer films. — •Norman Mechau, Marina Saphiannikova, and Dieter Neher — University of Potsdam, Institute of Physics-Soft Matter Physics, Am Neuen Palais 10, 14469 Potsdam

Photoinduced changes in the mechanical and dielectric properties of azobenzene polymer layers were measured utilizing the method of electromechanical spectroscopy. The measurements revealed a strong correlation between the time dependent behavior of the plate compliance and the dielectric constant under irradiation. Actinic light causes a light softening of the film, whereas ultraviolet irradiation results in an initial plasticization of the film followed by its hardening.

A semi-quantitative model based on the kinetics of the photoisomerization process in azobenzene polymers is proposed. We assume that both visual and ultraviolet irradiation increases the free volume in the layer due to photoisomerization. Additionally, ultraviolet light increases the modulus of the polymer matrix due to the presence of a high density of azobenzene moieties in the cis state. These assumptions allowed us to reproduce the time dependent behavior of the bulk compliance at different irradiation intensities, both for visual and ultraviolet light, with only two adjustable parameters.