Dual-Stage Supercritical CO₂ Foaming for Sequential Structural Conversion in High-Performance Reentrant Foam with Reversible Thermal-Induced Transformation

The controllable design and optimization of porous structures can endow the foam with unique functionalities and expand its application domains. In this work, we propose a dual-stage supercritical carbon dioxide foaming technology that leverages the synergistic effects of the pressure difference inside and outside the cells and the surface tension between the polymer matrix and gas, enabling direct conversion from engineering plastic polymer with a rigid molecular chain to the closed-cell reentrant foam. Using polycarbonate siloxane copolymer (Si-PC) resin as a matrix, we successfully prepared the reentrant concave angle Si-PC foam (R-PCF) with various transformation degrees by adjusting key process parameters in both first and second stages. R-PCF features a unique reversible thermal-induced structural transformation, excellent thermal insulation performance (the final temperature is 68 °C lower than the hot table and 17 °C lower than the Si-PC foam under stable heat source conditions), and chemical resistance. Additionally, the introduction of the reentrant concave angle structure effectively optimizes energy transfer pathways, making the R-PCF have superior energy absorption properties, improving the competitiveness of R-PCF for potential applications in thermal switches, intelligent thermal-drive devices, and protective and thermal management fields.