Crystallization‐Tuned Polymeric Phase‐Change Fibers with High Encapsulation Efficiency and Stability for Smart Thermal Managements

ABSTRACT Under the urgent demand for sustainable energy solutions, phase‐change fibers (PCFs) offer substantial potential for thermal energy storage through the reversible phase transitions. However, the limited solar energy utilization, constrained thermal storage capacity, and the trade‐off between encapsulation efficiency and stability impede the broad applications of PCFs. To address these challenges, we herein developed a coaxial microfluidic spinning device to precisely control the fiber size and crystalline structure by regulating the flow rate and composition of polymer solutions, achieving a high phase‐change enthalpy of 155.4 J/g and a large encapsulation efficiency of 74.4% in the resulting PCFs. Additionally, the crystalline structure of biodegradable poly(lactic acid) sheath was tuned by the stereocomplex crystallization of its two stereoisomers, leading to the enhanced mechanical, barrier property of fiber sheath and the improved stability of PCFs. Furthermore, the incorporation of cesium tungsten oxide nanoparticles as infrared absorbers enhanced the efficient capture of solar energy, the thermal conduction, and crystallinity of PCFs. The PCF fabrics demonstrated exceptional thermal storage and regulation capabilities on the house model and skin surface. This work offers an effective and scalable strategy for developing high‐performance PCFs towards smart thermal management.