Acid treatment of silver flake coatings and its application in the flexible electrical circuits

This work reports the preparation of a highly-conductive silver coating using silver micro flakes via a facile method of acid treatments. In this method, micron-sized silver flakes, suspended in isopropanol alcohol at 1 wt%, were deposited on polypropylene substrates, forming a silver coating with a surface coverage of ~7 × 10−10 g/m2. This coating was initially non-conductive. It was found that through a simple acid treatment by either immersing the coating in HCl solutions or exposing the coating to HCl vapors for a brief period <30 min, the conductivity of the coating could be improved dramatically, reaching a conductivity as high as ~3.8 × 104 S/cm. To investigate the mechanism, different solutions (acid, alkali and salts) were tested. The results indicated that both the Cl− and H+ ions were responsible for the increased conductivity, likely by partially replacing or removing the lubricant layers coated on the silver flakes. Furthermore, we applied this method to fabricate flexible electrical circuits by embedding silver patterns in plastic sheets or polydimethylsiloxane elastomers. The resultant circuits were conductive and bendable without losing conductivity, showing a good potential application in soft electronics.