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This paper reports on the synthesis and characterization of a novel class of materials namely, photo-actuating and photo-rheological polymers. The terms photo-actuation and photo-rheological refer to the phenomena, where photo-responsive polymers undergo conformational changes upon UV irradiation. This conformational change can result in changes in the spectral and physical properties of the polymer. For example, its volume and rheological properties. The first part of this paper describes the laboratory-based synthesis and characterization of these materials. The second part describes the experimental methodology and results obtained when characterizing the photo-actuation and photo-rheological behavior of the materials. It was paramount in these experiments to control the temperature of the test specimen; this was necessary as some of the changes in the properties brought about by UV irradiation could also be accounted for by an increase in the temperature of the test specimen.
Two classes of photo-responsive material were synthesized and characterized using conventional analytical techniques. The first series of polymers were polymethyl methacrylate (PMMA) based with azobenzene groups in the side chain, the second series contained spiropyran groups in the side chain. The characterization of the photo-rheological behavior of these materials involved the deployment of a custom-modified rheometer, which was operated under isothermal conditions. A liquid light guide was used to enable in-situ irradiation of the test specimen with UV or visible light. The photo-actuation studies involved experiments on liquids and solid films of the above-mentioned co-polymers. A commercially available 3-D surface profiler was used to study their photo-actuating behavior. A couple of unique apparatus were also designed and used to characterize the photo-actuation behavior of the polymers in solution.
The effects of irradiation on the photo-rheological and photo-actuating behavior were quantified taking temperature effects into consideration. Potential end-use applications for these polymers are considered.
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