In order to reliably print complex electronic circuitry, design rules or models that allow us to precisely estimate the printed patterns on non-wetting substrates are required. As we can intuitively imagine from ‘non stick kitchenware’, controlling the shape of liquid is very challenging. In these works, I experimentally found that contact angle hysteresis plays a significant role in printed two-dimensional feature patterning. In addition, I developed a simple hydrostatic model that determines printability of printed films in different size and printing parameters, and provided a basis for more complete methodology for inkjet printed films.
As shown in the pictures below, two glass substrates assumed to be identical based on equal equilibrium contact angles showed completely different inkjet printability: One (below left) showing precisely controllable shapes, but the other (below right) showing dewetting of the printed film and splitting into smaller circular patterns. We found that contact angle hysteresis plays a key role in controlling dewetting / advancing of the contact lines of inkjet printed films.
With wider contact angle hysteresis (left sample) due to nearly zero receding contact angle, printed pattern avoids the dewetting/breakup. A simple hydrostatic model of inkjet printed liquid lines with constant drop spacing was analytically driven to compare the contact angle of the feature with contact angle hysteresis window as shown below. The model predicted the “quality" of the printed films with different size and drop spacing quite well, defining three regions: Stable printing region; film separation region; and bulging region where the contact line advances and the shape becomes more circular.
The knowledge learnt from the inkjet printed film study was also applicable to gravure printed films as shown below. With widening contact angle hysteresis window by longer UV/Ozone surface treatment, we were able to avoid dewetting of the gravure printed films, and successfully print pinhole-free dielectric layer films.
Application to functional nanomaterial printing
Transferring the knowledge of the effect of contact angle hysteresis and contact line pinning on precision printing, we have also developed a universally applicable biocompatible surface coating process for precision printing of functional nano materials (bio-functional, plasmonic etc.). We have discovered that a polyelectrolyte layer-by-layer coating process can easily implement the contact line pinning effect regardless of the initial hydrophobicity of the substrate surface. In addition
Related Publications & Presentations
- Hongki Kang, Gu-Haeng Lee, Hyunjun Jung, Jee Woong Lee and Yoonkey Nam, “Inkjet-Printed Bio-Functional Thermo-Plasmonic Interfaces for Patterned Neuromodulation,” ACS NANO, 12, 2, 1128–1138, 2018.(Link)
- Hongki Kang, Gu-Haeng Lee and Yoonkey Nam, “Inkjet-Printed Gold Nanorods using Biocompatible Polyelectrolyte Layer-by-Layer Coating for Patterned Photothermal Applications,” 39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2017 (EMBS ’17), 3545–3548, 2017.(Link)
- Dan Soltman, Ben Smith, Hongki Kang, S.J.S. Morris, and Vivek Subramanian, “Methodology for inkjet printing partially wetting films," LANGMUIR, 2010, 26 (19), pp 15686-15693. (Link)
- Hongki Kang, Dan Soltman, and Vivek Subramanian, “Hydrostatic Optimization of Inkjet-Printed Films," LANGMUIR, 2010, 26(13), 11568-11573. (Link)
- PhD dissertation: Gravure-printed Highly-scaled Organic Thin-film Transistors for Low-cost and Large-area Electronics
- Dan Soltman, Ben Smith, Hongki Kang, Stephen Morris, and Vivek Subramanian, “Methodology for Inkjet Printing Partially Wetting Films," IS&T Digital Fabrication conference, Austin, TX, Sept. 19-23, 2010.
- Dan Soltman, Ben Smith, Hongki Kang, Stephen Morris, and Vivek Subramanian, “Methodology for two dimensional pattern generation in inkjet printing," LOPE-C, Messe Frankfurt, Germany, May 2010.
- Hongki Kang, Dan Soltman, and Vivek Subramanian, “Hydrostatic concerns in inkjet-printed films," Materials Research Society, San Francisco, US, Spring 2010.
- Dan Soltman, Hongki Kang, and Vivek Subramanian, “Considerations for pattern generation in inkjet-printed electronics," SPIE Advanced Lithography, San Jose, US, Feb 2010.