Robust photonically sintered self-assembled metallic nanofilms with substrate-dependent electromechanical properties for hypersensitive strain sensors
Solution-processed ultrathin nanocomposite conductors are attractive for wearable strain sensors due to cost-effectiveness and scalability, but achieving high sensitivity at low strains remains challenging because of polymer-induced hysteresis and uncontrolled crack formation. This work reports a robust, uniform, highly conductive silver nanofilm fabricated via layer-by-layer (LbL) assembly of positively charged polyurethane and uniformly sized silver nanoparticles (AgNPs) on various substrates, followed by photonic sintering to fuse the AgNPs into a cohesive structure and mitigate heat-induced cracks from elastomeric substrate expansion. The resulting Ag nanofilms achieve a conductivity of 5.1×10^4 S cm^-1 and exhibit substrate-dependent electromechanical properties. On oxygen plasma-treated polydimethylsiloxane (PDMS), the films function as hypersensitive strain sensors with gauge factors exceeding 3000 at strains below 5%, while on (3-aminopropyl)triethoxysilane-modified PDMS or thermoplastic elastomers, they remain stretchable with small resistance variations up to 50% strain. Mechanistic studies reveal that substrate surface chemistry governs crack propagation and interfacial adhesion, dictating sensing performance. The ultrasensitive sensors on PDMS enable detection of sound frequencies, pulses, and small forces, demonstrating potential for personalized health monitoring and human-machine interfaces. This approach offers a scalable route to high-performance, solution-processed strain sensors with tunable sensitivity and stretchability.