Progress on research and applications of polymeric foams and porous functional materials

Polymeric foams and porous materials are lightweight polymeric materials with a porous structure, also known as polymeric foams. Depending on the connectivity of the pores, polymeric foams can be classified into closed-cell and open-cell structures. The properties of open/closed-cell polymeric foams are determined by the polymer matrix, pore structure, and gas/cell wall interface characteristics. The diverse polymer matrices and rich pore structures endow polymeric foams with numerous functions, making them play a vital role in daily life and industrial production. Supercritical fluid physical foaming is a method for preparing polymeric foams using nitrogen or carbon dioxide supercritical fluids as physical foaming agents. This technology has gained increasing attention in academia and industry due to its environmentally friendly process, uniform and tiny cell structure of the prepared foam materials, and diverse preparation methods. Nonetheless, the foam materials obtained by supercritical fluid physical foaming are mainly closed-cell. The preparation of polymer porous materials with an open-cell structure can be achieved by selecting phase separation and ice templating methods. With the help of phase separation, polymer porous materials can be composited with more nanofillers to achieve superior functionality. This review summarizes the systematic work of the research group on the preparation of polymer/graphene oxide composite porous materials by phase separation. Up to 10wt%-30wt% of graphene oxide can be uniformly or selectively dispersed in the polymer porous materials through phase separation, endowing the polymer composite porous materials with good electromagnetic shielding effectiveness and electromagnetic wave absorption characteristics. This is beneficial for reducing electromagnetic wave leakage and the resulting secondary pollution problems. The porous structures obtained by physical foaming and phase separation often exhibit a relatively uniform distribution, but the orientation degree of the cell structure is low, and the pores cannot be interconnected. Directed freezing technology based on the ice templating method provides a way to obtain highly ordered pore structures in polymer systems. With the help of directed freezing technology, ordered porous foams with a single scale can be constructed, exhibiting excellent liquid adsorption performance. These ordered porous foams have tremendous application prospects in areas such as rapid liquid adsorption, active liquid transportation, and oil-water separation. Driven by the "dual carbon-driven high-quality development" strategy, low-carbon foaming technology using supercritical fluids as green foaming agents has gained market recognition. A large number of related research and development products have continuously moved from the laboratory to the market, and polymer foams and porous materials have received more attention. However, there are still many problems and challenges in the field of polymer foaming and porous materials that need to be urgently addressed: (1) Focusing on evolving application scenarios, developing polymer foam materials with specific geometric shapes (such as polymer microporous films, polymer microporous fibers, etc.) and special functions (such as low dielectric properties to meet 5G and 6G applications), and conducting in-depth research on material structure-property relationships to meet material application requirements; (2) innovating pore-forming methods and developing high-performance polymer foams and porous functional materials with the help of biomimetic design principles; (3) fully utilizing the advantages brought by the pore structure to polymeric materials and developing multifunctional and smart materials.