Double-Shell-Encapsulated Phase Change Materials with ZIF-8/SiO ₂ for Synergistic Thermal Regulation in Smart Wearable Textiles

Maintaining thermal comfort in extreme environments remains a significant challenge. Phase change materials (PCMs) offer a promising solution by absorbing and releasing heat during phase transitions; however, their practical application is often limited by low thermal storage capacity and leakage issues. In this study, we report the development of dual core−shell PCM composites by encapsulating a high-volume fraction of PCM within a porous ZIF-8 framework, followed by the controlled growth of an outer protective SiO2 shell. By varying the ZIF-8 amount (10−20 mg/mL), we optimized the composite structure and performance. Among the encapsulated PCMs (i.e., PS, PZ-10, PZ-15, and PZ-20), the composite with a 15 mg/mL loading (PZ-15) exhibited the most favorable thermal characteristics, including a melting temperature (Tm) of 34.86 °C, an enthalpy of fusion (ΔHm) of 102.4 J/g, a crystallization temperature (Tc) of 25.57 °C, and an enthalpy of crystallization (ΔHc) of 101.3 J/g. The prepared composite also demonstrated high thermal efficiency (η = 68.31) and encapsulation efficiency (ee = 66.94%), indicating excellent energy storage capacity and structural integrity. When applied to textile fabrics, PZ-15 enabled effective thermal regulation, maintaining surface temperatures ∼5.7 °C lower during heating and ∼6.0 °C higher during cooling compared to uncoated fabric. These results highlight the potential of double-shell (ZIF-8/SiO2)-encapsulated PCMs as thermally stable and leakage-resistant materials for next-generation wearable thermal management applications such as sportswear.