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Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions

Nature Chemistry volume 9, pages 145–151 (2017)Cite this article

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Abstract

The development of polymers with switchable glass transition temperatures (Tg) can address scientific challenges such as the healing of cracks in high-Tg polymers and the processing of hard polymers at room temperature without using plasticizing solvents. Here, we demonstrate that light can switch the Tg of azobenzene-containing polymers (azopolymers) and induce reversible solid-to-liquid transitions of the polymers. The azobenzene groups in the polymers exhibit reversible cis–trans photoisomerization abilities. Trans azopolymers are solids with Tg above room temperature, whereas cis azopolymers are liquids with Tg below room temperature. Because of the photoinduced solid-to-liquid transitions of these polymers, light can reduce the surface roughness of azopolymer films by almost 600%, repeatedly heal cracks in azopolymers, and control the adhesion of azopolymers for transfer printing. The photoswitching of Tg provides a new strategy for designing healable polymers with high Tg and allows for control over the mechanical properties of polymers with high spatiotemporal resolution.

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Figure 1: Chemical structure, photoisomerization and photoinduced solid-to-liquid transition of azopolymer P1.
Figure 2: Photographs of P1 in the sample preparation processes and photoswitchable Tg values of P1 studied by DSC.
Figure 3: Photoinduced liquid-to-solid transition of cis P1 demonstrated by photographs and rheology tests.
Figure 4: Reversible photoinduced solid-to-liquid transition of P1 in a spin-coated film studied by scanning force microscopy.
Figure 5: Chemical structures of three azopolymers and photoinduced solid-to-liquid transitions of these azopolymers studied by optical microscopy.
Figure 6: Healing, reduction of surface roughness and transfer printing based on photoinduced solid-to-liquid transitions.

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Acknowledgements

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, WU 787/2–1). H.Z. was supported by the MPG-CAS Joint Doctoral Promotion Programme (DPP). C.X. was supported by the CSC programme. S.H. and G.K.A. acknowledge support by DFG through SPP 1681, project no. AU321/3-1. The authors thank G. Fytas, G. Floudas and T. Bereau for helpful discussion and G. Kircher, U. Rietzler, J. Thiel and A. Hanewald for technical support.

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  1. Hongwei Zhou, Changguo Xue and Philipp Weis: These authors contributed equally to this work

Authors and Affiliations

  1. Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, 55128, Germany

    Hongwei Zhou, Changguo Xue, Philipp Weis, Yasuhito Suzuki, Shilin Huang, Kaloian Koynov, Günter K. Auernhammer, Rüdiger Berger, Hans-Jürgen Butt & Si Wu

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  1. Hongwei Zhou
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Contributions

S.W. conceived the idea and led the project. S.W., K.K., G.K.A., R.B. and H.-J.B. designed the experiments. H.Z., C.X., P.W., Y.S., S.H., K.K., R.B. and S.W. performed the experiments and analysed the data. All authors wrote the paper. H.Z., C.X. and P.W. contributed equally to this work.

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Correspondence to Si Wu.

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Zhou, H., Xue, C., Weis, P. et al. Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions. Nature Chem 9, 145–151 (2017). https://doi.org/10.1038/nchem.2625

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