Custom tailoring of conductive ink/substrate properties for increased thin film deposition of poly(dimethylsiloxane) films

The creation of more robust biocompatible printed electronics devices requires an understanding of interactions between conductive inks and substrates to achieve desired printing and functional properties. In this study, we present a water-based conductive ink that can provide a readily achieved thin film deposition on a highly hydrophobic surface such as poly(dimethylsiloxane) (PDMS). We also show that surface treatments with atmospheric plasma can be utilized to tailor the surface energy of hydrophobic substrates to improve the deposition of inks not custom made for such applications. By using a tailored Ag nano-particle ink, we have successfully printed conductive traces onto a hydrophobic (PDMS) substrate without any surface modification. It was also shown that when introducing atmospheric plasma treatment to the PDMS substrate prior to printing with the tailored ink poor printing resulted. The proposed mechanism for the cause of this poor wetting and deposition is an adverse interaction between the ink and PDMS surface caused by surface oxidation resultant of plasma treatment. The results show that the generally accepted rule that a difference between the substrate and ink surface energy of 10 mN/m for good print quality does not necessarily hold true in the case of functional printing.