Photodeformation behavior of photodynamic polymers bearing azobenzene moieties in their main and/or side chain

This paper describes a comparative study of polymers containing push-pull type azobenzene moieties in their main and/or side chains. The polymers were systematically designed and synthesized specifically for this work in order to investigate their photodeformation through the migration of polymer chains, which was induced by an optical field generated around some polystyrene (PS) spheres. The PS spheres, which had a diameter of 990 run, were arranged on the surface of the photodynamic polymer films by a self-organization process, and the films were then exposed to a linearly polarized Kr-Ar laser at 488 nm. Although the azobenzene moieties in the polymers exhibited a remarkably slow trans-cis-trans isomerization cycle, a series of hexagonally arrayed indented structures that reflected the geometry and arrangement of the spheres were successfully observed using atomic force microscopy (AFM). The depths of these dents were consistent with the dynamics of the azobenzene moiety in the polymers. The molecular weight, glass transition temperature (T-g), and absorptivity at the wavelength of the irradiating light were nearly identical for all of the materials that we used. However, the total amount of mass transport that occurred on the polymer surfaces did not depend directly on the efficiency of the photoisomerization, which was more related to the structure (i.e., main- or side-chain type) of the polymers. Furthermore, analysis of the polymer migration using tapping mode atomic force microscopy (TMAFM) revealed that the mechanism of the mass transport was clearly between the main- and the side-chain type polymers, which may be due to differences in the migration mechanism of the polymer chain.