Designing functional filler networks via in situ silver nanoparticles through barrier tuning and volume exclusion.

The fabrication of high-performance functional polymer composites requires delicate balance between functionalities, filler content and overall performance, and preparation route is urgently needed. Guided by Simmons theory, a PDMS-based stretchable conductor with metal-level conductivity is realized through a strategy by combining silver nanoparticle in-situ formation, optimized barrier height and volume excluding effect. Firstly, a universal matrix-independent etching-reduction method generates uniform Ag nanoparticles (~ 9.7 nm), shortening tunneling distances. Then, tunneling barrier height is minimized to 0.06 eV by aligning energy levels of surface-treated silver nanoflakes and PDMS, reducing electron scattering. Finally, silver-plated PDMS microspheres act as volume-excluding phase, compressing tunneling widths below the critical threshold (<10 nm). This integrated approach yields exceptional electrical conductivity (29429 S/cm) at 50 wt% Ag loading. Such tunneling networks retain 53% conductivity at 100% strain, while thermal conductivity increases from 4.3 to 24.3 W/m·K. This work demonstrates rational quantum tunneling barrier control to overcome performance trade-offs, providing a design framework for advanced conductive composites.