Substrate-Independent Surface Energy Tuning via Siloxane Treatment for Printed Electronics

Abstract

Digital printing enables solution processing of functional materials and opens a new route to fabricate low-cost electronic devices. One crucial parameter that affects the wettability of inks for all printing techniques is the surface free energy (SFE) of the substrate. Siloxanes, with their huge variety of side chains and their ability to form self-assembled monolayers, offer exhaustive control of the substrate SFE from hydrophilic to hydrophobic. Thus, siloxane treatment is a suitable approach to adjust the substrate conditions to the desired ink, instead of optimizing the ink to an arbitrary substrate. In this work, the influence of different fluorinated and nonfluorinated siloxanes on the SFE of different substrates, such as polymers, glasses, and metals, are examined. By mixing several siloxanes, we demonstrate the fine tuning of the surface energy. The polar and dispersive components of the SFE are determined by the Owens-Wendt-Rabel-Kaelble (OWRK) method. Furthermore, the impact of the siloxanes and therefore the SFE on the pinning of droplets and wet films are assessed via dynamic contact angle measurements. SFE-optimized substrates enable tailoring the resolution of inkjet printed silver structures. A nanoparticulate silver ink was used for printing single drops, lines, and source-drain electrodes for transistors. These were examined in terms of diameter, edge quality, and functionality. We show that by adjusting the SFE of an arbitrary substrate, the printed resolution is substantially increased by minimizing the printed drop size by up to 70%.

Siloxane-functionalised surface patterns as templates for the ordered deposition of thin lamellar objects

“…An example is the high throughput analysis in droplet microarrays, where discontinuous dewetting fills individual wells without mechanical containment 9,10 . In printed electronics, the deposition of functional inks constrained by hydrophobic barriers allows the creation of smaller structures 11 and the tailoring of surface properties to the requirements of different inks 12 . In technical applications, surface functionalisation has been used to create hydrophilic binding site patterns for the self-assembly of sub-millimeter silicon chips onto hydrophobic substrates submerged in water 13 .…”

Electrohydrodynamic Jet Printing of One‐Dimensional Photonic Crystals: Part I—An Empirical Model for Multi‐Material Multi‐Layer Fabrication

“…It should be noted that a continuous jet‐printing mode can also be used to deposit material on the substrate similar to line printing in ref. [ 25 ] . However, the fabrication of uniform thin films (film spatial resolution < 100 × 100 µm, film thickness < 100 nm) requires the deposition of high‐resolution droplets (droplet diameter < 2 µm, droplet height < 100 nm).…”

“…Several previous studies have investigated how tuning the solid surface energy (SSE) of a substrate can affect droplet shape and subsequent feature resolution in inkjet printing. [ 25,27 ] This has been extended to high‐resolution e‐jet printing, where the microscale contact angles of droplets were used to predict the merging quality of lines [ 28 ] on varying SSE surfaces. Microscale contact angles (droplets of 2–10 µm) are also used here to predict the roughness of a deposited layer of a build material on the surface of a previously printed material.…”

“…The silicon wafer showed the highest average SSE (γ s = 66.3 mN m −1 ), followed by NOA170 (γ s = 48.3 mN m −1 ), while the lower index materials ( n L = 1.35–1.51) exhibited significantly lower SSE values (γ s = 11.5–19.5 mN m −1 ). From previous reports, [ 25 ] it is expected that a material with a high SSE value will be a more favorable substrate for realizing uniform film formation of the next layer. This supports our observations that NOA170 is a favorable substrate for the low index materials evaluated here.…”

Substrate Treatment Evaluation and Their Impact on Printing Results for Wearable Electronics

“…Among these, chemical bases treatment has been claimed to be cheaper and readily available solution for such surface modifications. Chemical treatment is ideally required for water-based solution and particularly for binding biomolecules on polymeric substrates (Schlisske et al, 2018;Santidrián et al, 2019). Carboxylic acid groups are created on the surface of polymer substrates as a result of chemical modification that enhances the attachment of bioactive molecules such as proteins onto the surface.…”