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, 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.