Paint-On Artificial Muscles: Cantilever Measurements of Stress and Efficiency of Photomechanical Coatings of Azo Polymers

The efficiency of the photomechanical effect in thin films of three azobenzene-based polymers PDR1A, PDR13A, and PMMA-co-PDR1A was determined using a cantilever-based sensor. The polymers were coated onto silicon and mica cantilevers, and the resulting cantilever bending under irradiation with visible light was measured to estimate changes in surface stress, photomechanical energy transduction per unit volume, and overall photomechanical efficiency. The photomechanical response was shown to be robust, repeatable, and quantifiable for all the polymers studied, even when the active polymer layer was much thinner than the cantilever substrate. Among the materials tested, PDR1A generated the largest forces, while PMMA-co-PDR1A exhibited the highest efficiency. For 35-µm-thick mica cantilevers coated with PDR1A, photoisomerization induced rapid and significant cantilever bending in the range of 100s of µm, corresponding to surface stress changes in the range of N/m. These results demonstrate the ability of thin azobenzene polymer films to function as strong, light-driven ‘artificial muscles’ in larger mechanical systems, and highlight the cantilever sensor platform as a powerful tool for the quantitative characterization of photomechanical effects in azo dye-based polymers.