Melamine Foams Decorated with In-Situ Synthesized Gold and Palladium Nanoparticles

In situ controlled and conformal coating of polydimethylsiloxane foams with silver nanoparticle networks with tunable piezo-resistive properties

Nanoparticle-polymer composites hold promise in enabling material functionalities that are difficult to achieve otherwise, yet are hampered to date by the scarce control and tunability of the nanoparticle collective properties on the polymer surface, especially for polymer foams featuring a complex three-dimensional pore network. Here we report on the controlled and conformal in situ coating of polydimethylsiloxane (PDMS) foams with silver nanoparticles (AgNPs) with surface coverage finely tunable over a large range, from 0 to 75%, via the one-step room temperature reduction of AgF directly on the PDMS surface. This enables the design of AgNP electrical networks on the PDMS foam surface with piezo-resistive properties tunable up to a factor of 1000. We leveraged the control of the piezoresistive properties of the AgNP electrical network formed on PDMS foams to fabricate flexible and wearable pressure sensors with sensitivity of 0.41 kPa^-1, an operation range >120 kPa, and a detection limit of 25 Pa. As a proof-of-concept application in wearable biomedical electronics, we successfully used the sensors to monitor the real-time radial artery pulse wave on the human wrist of a young male with high resolution.

Microwave Foaming of Materials: An Emerging Field

In the last two decades, the application of microwave heating to the processing of materials has to become increasingly widespread. Microwave-assisted foaming processes show promise for industrial commercialization due to the potential advantages that microwaves have shown compared to conventional methods. These include reducing process time, improved energy efficiency, solvent-free foaming, reduced processing steps, and improved product quality. However, the interaction of microwave energy with foaming materials, the effects of critical processing factors on microwave foaming behavior, and the foamed product's final properties are still not well-explored. This article reviews the mechanism and principles of microwave foaming of different materials. The article critically evaluates the impact of influential foaming parameters such as blowing agent, viscosity, precursor properties, microwave conditions, additives, and filler on the interaction of microwave, foaming material, physical (expansion, cellular structure, and density), mechanical, and thermal properties of the resultant foamed product. Finally, the key challenges and opportunities for developing industrial microwave foaming processes are identified, and areas for potential future research works are highlighted.