Session: 04-17-01: Functional Soft Composites - Design, Mechanics, and Manufacturing

Paper Number: 172857

Precisely Patterning Liquid Metal Microfibers Through Electrohydrodynamic Printing for Soft Conductive Composites and Electronics 

Liquid metal particle-based microfibers attract great interest in soft and wearable electronics. The most facile method to fabricate sub-50 µm liquid metal fiber is electrospinning. However, electrospinning has poor patterning ability and the electrospun fibers have inherent defects, which significantly lowers the electrical conductivity and limits their application. Therefore, better manufacturing methods are needed to precisely deposit high-quality liquid metal fibers.

In this work, an electrohydrodynamic (EHD) printing process is developed to precisely pattern liquid metal microfibers with minimal defects and ultra-high resolution (≈1.5 µm), overcoming the limitations of electrospinning. The developed printing process demonstrates high resolution, excellent patterning capability, and scalability. We have identified two main technical challenges in the EHD printing of liquid metal microfibers: a) arcing when printing on conductive substrates with conductive nozzles; b) poor fiber junction caused by residual charges when printing on non-conductive substrates. To eliminate arcing, we used glass nozzles as printing head instead to lower the electric field strength. To remove residual charges, we deposited carbon coating onto non-conductive substrates before printing. With these solutions, we successfully printed liquid metal microfibers on both conductive and non-conductive substrates. The typical width of the printed microfibers is 4–70 µm, with a minimum fiber width of 1.5 µm. To the best of our knowledge, the patterning resolution achieved in this work is the highest reported for liquid metal particle-based inks. In addition, by printing multiple layers, we obtained liquid metal fiber with a high aspect ratio (height/width >10).

The patterned liquid metal fibers can be used for soft conductive composites and soft electronics with highly customized microscale features. The conductive composites embedded with these fibers not only exhibit high conductivity (up to 214 S cm⁻¹), but also possess nearly strain-insensitive resistance (7.3% resistance change at 200% strain) and exceptional cyclic stability. Note that the stretchability can be further improved by choosing other elastomers. Overall, the developed composites retain the conductivity and the strain-insensitive behavior of particulate liquid metal composites with a very minimal amount of liquid metal.

Due to the exceptional properties, liquid metal-polymer microfibers and their composites are well-suited for various applications, such as soft and wearable circuits, stretchable sensors, transparent electrodes, and epidermal electronics. We demonstrated that the patterned liquid metal-polymer fibers can be utilized as electrodes for a multi-touch sensor. The fabricated sensor can accurately and reliably detect finger touch locations. For their composites, we showcased their usage as stretchable Joule heaters and transparent electrodes. The transparent electrodes we developed exhibit superior strain-insensitive behavior compared to other liquid metal transparent electrodes in the literature.

Presenting Author: Pu Zhang State University of New York at Binghamton

Presenting Author Biography: Pu Zhang is an associate professor of mechanical engineering at State University of New York at Binghamton since 2018. Before Binghamton, he worked as a postdoctoral researcher at University of Manchester in the U.K., earned a PhD (2015) in mechanical engineering at University of Pittsburgh in the U.S., and received BS (2008) and MS (2011) in mechanics from Hunan University in China. His research focuses on the mechanics, design, and manufacturing of soft functional materials with tailored microstructures for desired mechano-physical properties. He has published 40+ refereed journal articles in mechanics and manufacturing journals. He received the NSF CAREER Award in 2022.

Authors:

Pu Zhang State University of New York at Binghamton
Jiexian Ma State University of New York at Binghamton
Zihan Liu State University of New York at Binghamton