Laser-patterned gold-leaf/WPU conductive films for flexible electronics

Gold is typically used as conductive layers in wearable electronics because of their good conductivity and chemical stability; however, the weak adhesion between gold films and flexible substrates is a persistent engineering issue. In this report, we introduce a convenient and unique process for preparing flexible conductive films compounded with traditional gold leaf of 110-nm thickness and waterborne polyurethane (WPU) film, which meet the highest ASTM class standard of 5B and has excellent adhesion strength (not less than 440 N/m) between the gold leaf and the WPU film. The resulting gold-leaf/WPU conductive film (GWCF) exhibits excellent conductivity (1.14 ×10⁷ S/m) and a sheet resistance of 0.8Ω/sq and a 50 % stretchable working range, GF (61.3). The average adhesion strength of the gold leaf on the WPU film (prepared via in-situ polymerization) was 1257 ± 50 N/m. The sensor withstood 2000 finger frictions and 500 contact frictions, maintaining stable resistance without significant changes, and was successfully developed into strain sensors for gesture recognition. Furthermore, rear-side laser ablation method was used for high-precision patterning of gold leaf (with minimum line width of 50 µm and minimum line pitch of 25 µm), resulting various flexible electrodes of shapes. The flexible humidity sensor with interdigital electrode of GWCF and graphene oxide shows high sensitivity, repeatability, and stability under bending; and GWCF-based flexible circuits offer high transparency, waterproofing, and stable deformation, with applications in wearables and fabric-integrated LED circuits. Additionally, a flexible smart remote controller using GWCF was developed for omnidirectional control of a smart vehicle via Bluetooth, enhancing human-machine interaction. In summary, this study presents an easy and cost-effective approach to fabricating flexible gold electrodes with great potential for flexible electronics applications.