A nature-inspired glue for writing liquid metal ink onto any surface
(Nanowerk News) Room temperature liquid metals, such as gallium and its alloys, are fascinating materials due to their unique combination of metallic and fluidic properties, that most certainly reminds one the Hollywood blockbuster movie Terminator 2: Judgment Day in 1992. The self-healing, shape-changing robot might have seemed surreal with a sci-fi visual effect that time, however, current research in liquid metals is closing the gap from reality.
Liquid metals have been at the forefront of developing next-generation flexible electronics, actuators, sensors, and robotics. For many of such applications, writing/patterning of liquid metals is a key processing step, of which, the efficiency and ease of operation are of critical importance. However, patterning of liquid metals onto different surfaces is not easy.
The current liquid metal inks suffer from undesired inconsistency of writing, operational complexity, and most importantly, regardless of the applied strategy, the choice of surface for consistent patterning are extremely limited at present.
Written traces with the sticky liquid metal ink. (Image: UNSW)
“Surface specificity during writing with liquid metal ink is a serious challenge that stems from the high surface tension of these liquid metals. Solving this problem with inexpensive adhesives and a simple methodology can be a game-changer.” Prof. Kourosh Kalantar-Zadeh (UNSW Sydney), who is one of the corresponding authors of the paper, commented.
The inspiration of this study though, came from a very different angle. In nature, various marine invertebrates (for example, mussels) survive in strong tidal environments, by secreting gluey substances that stick them to any solid surfaces. The functional group known as catechol in the glue, is responsible for such adhesion.
Interestingly, this very group are also prevalent in plant kingdom, in the form of compounds named polyphenols—regularly found in our dietary chain such as tea, chocolate, and wine. The team used tannic acid, a polyphenol, as the molecular glue for the liquid metal ink preparation.
The writing method is simple, put the ink into a regular ballpoint pen and write words or design patterns as you wish. And the choice of surface is unlimited, as the sticky inks can be applied onto a wide range of substrates with varying surface chemistries and physical properties.
The team further explored the potential applications of the sticky inks, for stretchable electronics, touch and toxic metal sensors.
“This approach of liquid metal patterning, enabled by an abundant natural polyphenol with universal adhesion properties, takes advantage of the fundamental interfacial chemistry of liquid metals and polyphenols. The developed concept can be used as a general platform to fabricate smart sensors, advanced electronic devices and functional materials in a surface-independent manner to create technologies of the future.” Dr. Md. Arifur Rahim (UNSW Sydney), the lead author of this study, said.