Inkjet printing of triethylene glycol monomethyl ether (TEGMME)-based ink droplet on oxygen plasma treated PDMS substrate for flexible circuit

Abstract

Circuits fabricated by inkjet printing on polydimethylsiloxane (PDMS) substrate is a promising direction of flexible electronics. Oxygen plasma treatment is a commonly used method to modify PDMS from hydrophobic to hydrophilic, which is prerequisite before inkjet printing. In this study, inkjet printing of triethylene glycol monomethyl ether (TEGMME)-based silver dispersion nanoparticle droplets on oxygen plasma treated PDMS was investigated by molecular dynamics simulations and experiments. It is revealed that the improved hydrophilicity of PDMS surface is contributed to the replacement of hydrophilic groups (-OH and -C=O) from hydrophobic groups (-CH3) on the PDMS molecular chains. Considering the existence of hydroxyl groups in TEGMME molecules, more hydrogen bonds are formed at the interface between the treated PDMS and TEGMME-based droplets during printing process. These significantly optimize the merging of droplets and the distribution of silver nanoparticles. Moreover, too short plasma treatment will lead to poor circuit morphology caused by weak hydrophilicity, while too long treatment will lead to defects caused by coffee ring effect. The suggested process parameter is treating PDMS for 30 s at a radio-frequency power of 45 W. The morphology of printed circuit is greatly improved and the resistivity decreased to 2.5 Ω/mm. A PDMS-based pressure sensor is designed and fabricated by the proposed inkjet printing process, which shows a sensitivity of 1.8 Ω/kPa and R2 of 0.98.