Title: Regulating the Photodeformation Behavior of Azobenzene-Containing Polyimide via Thermal Treatment

Author: Menghan Zhang, Xuejie Sun, Jia Wei*, Yanlei Yu

Journal: ACS Appl. Polym. Mater. 2024, 6, 12261−12268

Abstract:

Photodeformable polymers have signiffcant potential for untethered smart actuation due to their rapid response and versatile deformation behaviors. However, altering deformation behaviors typically requires preparing materials with different macromolecular structures. Here, we achieved controllable reversal of photodeformation behaviors (bending away from or toward the light source) in side-chain azobenzene polyimides by adjusting the thermal treatment conditions. Different thermal treatments introduced variations in the internal free volume of the material, leading to two distinct deformation mechanisms under blue light exposure and resulting in opposite macroscopic deformation behaviors. By choosing appropriate thermal treatment methods, we fabricated actuators with speciffc functionalities and utilized the correlation between deformation behavior and thermal treatment to demonstrate a detector for thermal history. This postsynthesis regulation of the photodeformation behavior offers a convenient and repeatable manner to engineer actuation on demand.

Fulltext Link: https://pubs.acs.org/doi/10.1021/acsapm.4c02399?ref=PDF

In this work, we present a method to easily enable the side-chain azobenzene polyimide to exhibit opposite photodeformation directions through thermal treatment. By applying rapid or slow cooling processes to the polyimide, different free volumes were introduced within the resulting polymer fflms. Under blue light irradiation, these differentiated free volumes led to distinct photodeformation mechanisms: for SC-PI, free volume expansion and for RC-PI, free volume contraction, resulting in opposite deformation behaviors. This variation in the free volume provides the polyimide with unique deformation characteristics, enabling a reversible switch in the bending direction. The principles elucidated here have the potential to advance the development of adaptive materials capable of complex, programmable responses to environmental stimuli and transform the design of smart devices and sensors that requireprecise bidirectional control.