Molecular dynamics simulations on photoinduced switchable Tg and self- healing behaviors of azobenzene-containing polymers

YQ Zhang and H Yang and YG Sun and XR Zheng and YF Guo, COMPUTATIONAL MATERIALS SCIENCE, 215, 111810 (2022).

DOI: 10.1016/j.commatsci.2022.111810

Developing polymers with switchable glass transition temperature (Tg) can solve scientific challenges such as fracture healing of polymers with high Tg and processing of hard polymers without plasticizer at room temperature. The azobenzene-containing polymers, or the so-called azopolymers, are smart materials that show photoswitchable Tg and photoinduced motions, which can be used in fabrication of photoactuators. Here, healable and reprocessable models were constructed by using linear azopolymers. Molecular dynamics (MD) simulation was used to study the behaviors of photo-induced bending, self-healing, and directional photofluidization of the azopolymers. A temporary modification of the C-N=N-C dihedral potential was applied to achieve the isomerization of azopolymer by using polymer consistent force-field (PCFF). The simulation results show that isomerization of azobenzene groups can lead to photoswitchable Tg of the azopolymers, which resulting in shape changes and different mechanical responses. Furthermore, the photoswitchable Tg makes the azopolymers much easier to heal under UV irradiation, and restore the mechanical properties under visible light irradiation. Finally, the mechanism of photoliquefaction was investigated, our results imply that the photoinduced trans-cis- trans cycles can reduce the mechanical properties and Tg values of azopolymers.

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