Elastomer foams with switchable folded cellular structure for EMI shielding, comprehensive sealing, and cushioning protection

Multifunctional electromagnetic interference (EMI) shielding materials delivering comprehensive and customized protection in complex environments is still a change. Herein, a folded cellular structure was incorporated into polyolefin elastomers/olefin block copolymers/carbon nanostructures (POE/OBC/CNS) foams through supercritical CO₂ foaming combined with vacuum treatment. The volume of the foams could be stored and released through the conversion between conventional cellular structure and folded cellular structure, which could not only manipulate the EMI shielding and mechanical performance but also provide an excellent sealing effect to avoid wave leakage and water penetration. Meanwhile, the expanded foam could effectively seal both regular and irregular components, preventing water penetration even when subjected to a mass of water 100 times greater than that of the foam, while also suppressing gas penetration under CO₂ exposure. After sealing, the EMI shielding effectiveness enhanced from 21.9 dB to 46.0 dB. The mechanism behind the folding and opening of the cells has been systematically analyzed. Due to the unique folded cell structure, the foam exhibited commendable traits in terms of flexibility and resilience, providing cushioning protection. With the above merits, the folded foams are promising for the development of advanced multifunctional EMI shields providing comprehensive protection.