High Cycle-Life Twistocaloric Cooling of Poly-p-Phenylene Benzodioxole Fibers.

It is an urgent need to develop efficient solid state cooling technologies and materials with high cycle life. Poly-p-phenylene benzodioxole (PBO) is a high performance fiber with excellent mechanical properties. In this work, for the first time, we report elasto- and twistocaloric cooling of PBO fibers by stretching and twisting of the PBO fiber bundles. The cooling temperature reached -0.4 K and -1.3 K, for fiber stretching and twisting, respectively. A self-coiled PBO fiber achieved maximum cooling of -3.7 K upon stretching by 35% strain, with an exceptionally high cycle life of 200,000 times. During the twisting of the PBO fibers, we observed reversible changes in the intensity of the diffraction peaks in X-ray diffraction patterns. A strain-sensitive color change application was realized by coating a self-coiled PBO fiber with liquid crystallite dyes. This work provides new perspectives for PBO fibers as a high cycle-life solid-state refrigeration material. This article is protected by copyright. All rights reserved.