Abstract
In this study, we investigated geometrical characteristics of the inkjet-printed lines with non-zero receding contact angle (CA) on plasma-treated substrates in terms of various printing variables and analyzed the fluidic behavior and hydrodynamic instability involved in the line formation process. The printing variables included surface energy, droplet overlap ratio, printing frequency, a number of ink droplets, substrate temperature and printing procedures. For the study, a colloidal suspension containing 56 wt % silver nanoparticles in tetradecane solvent was used as a printing ink. It has electrical resistivity of 4.7 μΩ·cm. The substrates were obtained by performing a plasma enhanced chemical vapor deposition (PECVD) process with C4F8 and O2 under various treatment conditions. As results of the experiments, the surface shape and pattern of the inkjet-printed Ag lines were dominantly influenced by the surface energy of the substrates, among the printing variables. Accordingly even when the receding CA was non-zero, bulging instability of the lines occurred forming separate circular patterns or regular bulges connected by ridges. It is a new finding of this study, which is completely different with the bulging instability of inkjet lines with zero receding CA specified by previous researches. The bulging instability decreased by increasing surface temperature of the substrates or employing interlacing procedure instead of continuous procedure for printing. The interlacing procedure also was advantageous to fabricate thick and narrow Ag lines with well-defined shape through overprinting on a hydrophobic substrate. These results will contribute greatly to not only the production of various printed electronics containing high-aspect-ratio structures but also the improvement of working performance of the devices.
Highlights
Inkjet printing of solution-processable materials has recently received much attention as a promising means to realize printed electronics
We investigate the peculiarity of formation of inkjet-printed lines with non-zero receding contact angle using silver colloidal ink
Contact angles are measured for each plasma-treated substrate using an optical contact angle analyzer (Phoenix 300, Surface Electro Optics Co., Ltd., Suwon, Gyeonggi-do, Korea)
Summary
Inkjet printing of solution-processable materials has recently received much attention as a promising means to realize printed electronics. Stinger and Derby demonstrated experimentally that the bulging instability depends on droplet spacing and print-head traverse velocity [24] They elaborated the phenomena physically in terms of the spreading flow due to capillarity and the pressure-driven flow co-existing in printed lines, without considering the hysteresis of contact angles of an ink droplet on a substrate. We investigate the peculiarity of formation of inkjet-printed lines with non-zero receding contact angle using silver colloidal ink It aims to explore the printing process which can produce stable liquid lines without fluid instabilities. The effects of various variables including surface energy, printing parameter, substrate temperature and printing procedure on the geometrical characteristics of inkjet-printed lines with non-zero receding contact angle are examined. It is attributed to the fact that the over-deposited droplets show different fluidic behaviors with ones on a flat surface, because of the undulated surface of the as-printed layer
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