High Cycle‐Life Twistocaloric Cooling of Poly‐p‐Phenylene Benzodioxole Fibers

Abstract 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, elasto‐ and twistocaloric cooling of PBO fibers by stretching and twisting of the PBO fiber bundles is reported. The cooling temperature reaches −0.4 and −1.3 K, for fiber stretching and twisting, respectively. A self‐coiled PBO fiber achieves 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, reversible changes in the intensity of the diffraction peaks in X‐ray diffraction patterns are observed. A strain‐sensitive color change application is 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.