Development of multiscale porous elastomer substrates with passive-cooling capabilities and strain-insensitive conductive nanocomposites for skin-interfaced electronics
[EMBARGOED UNTIL AUGUST 2023] Emerging skin-interfaced electronics have been playing a significant role in many areas such as clinical healthcare and mobile fitness tracking because they can collect a variety of biological signals from human body. However, conventional electronic materials are usually rigid and brittle, which leads to mechanical mismatch with soft human skin. To overcome the disadvantages, we paid attention to intrinsically stretchable polymer materials. This work focuses on the synthesis of novel multifunctional porous materials for breathable and intrinsically stretchable skin-interfaced electronics with minimal inflammation risks, outstanding mechanical pliability, and other desired features. We first report on the fabrication of multiscale porous elastomer supporting substrates with passive cooling properties which means the on-skin electronics made with the porous elastomer substrates can passively cool human bodies without energy consumption. It also exhibits other desired properties, including mechanical compliance, high breathability and waterproofing. The outstanding passive-cooling capability and breathability stem from the structural engineering of multiscale porous structure in elastomer, which was achieved by simple, cost-effective, and scalable phase separation-controlled process. We also demonstrate some applications of wearable skin-interfaced bioelectronics for continuous monitoring of human vital signals and human-machine interactions. These devices are patterned by spray printing of silver nanowires on prestretched multiscale porous polystyreneblock-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) substrates. Leveraging the same versatile synthesis approach, we then introduce the synthesis of strain-insensitive conductive nanocomposite, which is enabled by well-controlled in-situ distribution of conductive nanofiller (i.e., silver nanowires) on the surface of microscale pores. The judiciously engineered structure enables substantially decreased (~50 times) percolation threshold and excellent strain-insensitivity property. The obtained porous conductive nanocomposite also exhibits outstanding breathability, conductivity, strain-insensitivity, mechanical and electrical robustness and durability.