Photoisomerization of AzoBmapolymer induces fast and reversible high-to-low thermal conductivity transitions

The discovery of novel polymeric materials with variable heat transport properties could revolutionize the utilization and manipulation of thermal energy to keep devices working optimally. Here, we synthesized a poly-1-butyl-5-((4-(phenyldiazenyl)phenoxy)methyl)2-ethyl-2,4,4-trimethylpentanedioate (AzoBmapolymer) containing photoisomerization's groups through reversible addition-fragmentation chain transfer polymerization. Firstly, using a thermal conductivity (TC)-measuring instrument, we demonstrate the TC of photoresponsive AzoBmapolymer that reversibly switches between low (0.13 +/- 0.02 Wm(-1) K-1) and high (0.24 +/- 0.02 Wm(-1) K-1) states. And surprisingly, the 84.6% change of TC was achieved by the modulation of the AzoBmapolymer containing photoisomerization's groups through green and ultraviolet photoirradiation. What is more, our synthesized photosensitive AzoBmapolymer is capable of TC transition within 7 s controlled by photoirradiation, and its photoregulated TC transition rate is dozens or hundreds of times higher than that driven by magnetic field molecular orientation (0.17 h), electrochemical oxygenation (0.5 h), or temperature modulation (1 h). Theoretically, the photoisomerization's groups of AzoBmapolymer can lead to different spatial configurations of macromolecules. Meanwhile, this conformational transition results in a change in the pi-pi stacking (d(pi-pi)) spatial configuration and an amorphous-to-crystal transition. More importantly, X-ray diffraction, crosspolarized optical microscopy, and TC-measuring instrument jointly demonstrate that photoirradiation reversibly change the thermophysical properties of AzoBmapolymer phonon transport. In other words, this result illustrates a powerful manipulation of the thermophysical properties of the polymers by photoirradiation. The AzoBmapolymer could complement traditional metal heat transfer materials used in applications; for instance, heat exchangers, electronic packaging, and heat sink.

Automated summary

We synthesized a novel polymer material that can reversibly switch between low and high thermal conductivity states through photoisomerization. The material showed an 84.6% change in thermal conductivity through green and ultraviolet photoirradiation. The photosensitive polymer also demonstrated a fast transition rate controlled by photoirradiation, significantly higher than other methods such as magnetic field orientation, electrochemical oxygenation, or temperature modulation.