Hybrid method involving atmospheric plasma treatment and inkjet deposition for the development of conductive patterns on flexible polymers

In this study, the flexible polymer substrate polyethylene naphthalate (PEN) was modified under two different plasma chemistries, namely helium–oxygen (He–O2) and helium–water vapor (He–H2O) plasmas at atmospheric pressure and room temperature. Surface changes related to wettability, chemical functionalization, surface energy, and morphology after plasma treatment were investigated using water contact angle (WCA) goniometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Each plasma resulted in a more hydrophilic PEN surface, with WCA decreasing by 68% and 85% for He–O2 and He–H2O plasma treated PEN, respectively, after only 1.0 s of exposure. An aging study of plasma treated PEN shows an increase in WCA that is still 30° lower than that of the as-received PEN after 1 month. XPS and AFM results show that improved wettability of the plasma modified PEN is due to the oxidation of the surface and not due to the increased surface roughness. To promote a roll-to-roll process of atmospheric plasma treatment and inkjet deposition, printing was performed using the conductive polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) on the as-received and plasma treated PEN surfaces where the shape and morphology of the lines were studied. Each plasma treated PEN surface exhibited well-defined, uniform inkjet-printed lines due to the improved wettability and increased surface energy. After scanning electron microscopy (SEM) analysis of the PEDOT:PSS dispersion of a single drop on each substrate, the He–H2O plasma treated surface led to less agglomeration of PEDOT:PSS and a more homogeneous drop deposit.