A Multifunctional Closed-Cell Composite Foam: Temperature-Independent Dimensional Stability, Multi-Shape Memory, and Robust Electromagnetic Wave Absorption

With the rapid advancement in autonomous vehicles, 5G and future 6G communications, medical imaging, spacecraft, and stealth fighter jets, the frequency range of electromagnetic waves continues to expand, making electromagnetic interference (EMI) shielding a critical challenge for ensuring the safe operation of equipment. Although some existing EMI shielding materials offer lightweight construction, high strength, and effective shielding, they struggle to efficiently absorb broadband electromagnetic waves and mitigate dimensional instability and thermal stress caused by temperature fluctuations. These limitations significantly reduce their service life and restrict their practical applications. To address these challenges, this study introduces a novel cis-polybutadiene (PBD)/carbon black (CB)/Fe3O4 closed-cell foam utilizing expandable microspheres (EMs) as the foaming agent. The PBD matrix exhibits a two-way shape-memory effect (2W-SME), which counteracts conventional thermal expansion and imparts temperature-independent dimensional stability to the material. The excellent compatibility of PBD with CB and Fe3O4, combined with the closed-cell foam structure, ensures that the composite remains lightweight while delivering high specific mechanical properties. Additionally, the three-dimensional conductive network within the foam provides exceptional broadband EMI shielding and superior electromagnetic wave absorption capabilities. This work offers an innovative approach to designing foams that combine lightweight construction, high specific strength, stiffness, and toughness with temperature-independent dimensional stability, broadband EMI shielding, and robust electromagnetic wave absorption, paving the way for advanced material applications.