Creating Nanoknot-Like Domains for Robust Artificial Spider Silk Toward High Twistocaloric Performance.

Abstract

High-efficiency refrigeration materials with long cycle lifetimes are essential for reducing energy consumption in conventional cooling systems. Twistocaloric cooling, which harnesses nonlinear torsional stress, offers a promising pathway to enhanced cooling efficiency. However, a general design strategy for polymer-based twistocaloric materials that combine high efficiency and long cycle life remains elusive. Here, we report spider silk-inspired polybiurea elastomer fibers that exhibit exceptional mechanical properties and twistocaloric cooling performance. The material's architecture features nanoknot-like domains formed via multiple hydrogen bonds and π-π interactions in the hard segments, which knot together the soft segments to provide high mechanical stability and substantial entropy changes. The polybiurea fibers with nanoknot-like domains achieved an extraordinary combination of breaking strength of 316.5 MPa and toughness of 523.4 MJ m^-3. This engineered deformable knotted structure enables a maximum cooling temperature drop of -17.1 K (by twisting and stretching), a maximum Carnot efficiency of 89.7%, and operational durability up to 120 000 mechanical fatigue life cycles. We further demonstrate two out-of-phase operated twistocaloric devices designed to recover input mechanical energy, thereby enhancing overall system efficiency. This work presents a robust materials strategy for advancing high-performance polymeric refrigeration materials and systems.