Polyphenol‐Induced Adhesive Liquid Metal Inks for Substrate‐Independent Direct Pen Writing

Abstract

Surface patterning of liquid metals (LMs) is a key processing step for LM‐based functional systems. Current patterning methods are substrate specific and largely suffer from undesired imperfections—restricting their widespread applications. Inspired by the universal catechol adhesion chemistry observed in nature, LM inks stabilized by the assembly of a naturally abundant polyphenol, tannic acid, has been developed. The intrinsic adhesive properties of tannic acid containing multiple catechol/gallol groups, allow the inks to be applied to a variety of substrates ranging from flexible to rigid, metallic to plastics and flat to curved, even using a ballpoint pen. This method can be further extended from hand‐written texts to complex conductive patterns using an automated setup. In addition, capacitive touch and hazardous heavy metal ion sensors have been patterned, leveraging from the synergistic combination of polyphenols and LMs. Overall, this strategy provides a unique platform to manipulate LMs from hand‐written pattern to complex designs onto the substrate of choice, that has remained challenging to achieve otherwise.

3D Printable concentrated liquid metal composite with high thermal conductivity

“…This flow behavior as liquid makes LM a promising material candidate for various applications ( Bartlett et al., 2017 ; Dickey, 2014 ; Jeong et al., 2015 ; Palleau et al., 2013 ; Zhu et al., 2013 ) but limits its applications at the same time. This crucial limit of processability has created the need for various approaches for processing LM such as filling/removing LM into/from a tube ( Khan et al., 2014a , 2014b ; Lin et al., 2017 ), direct writing/3D printing of LM ( Ladd et al., 2013 ; Neumann and Dickey, 2020 ), direct writing of LM composite ( Neumann et al., 2020 ; Rahim et al., 2021 ), and 3D printing of carbon nanotube/LM composites ( Park et al., 2019a , 2019b ). Among these efforts, Ladd et al., reported the oxide layer of the LM allows the LM itself to be used as a 3D printable material ( Ladd et al., 2013 ).…”

3D Printable Electrically Conductive Hydrogel Scaffolds for Biomedical Applications: A Review

“…In a separate study, TA/EGaIn-LM composite dispersions were used as inks in a ballpoint pen for writing conducting patterns using a DIW 3D printer. The fabricated complex patterns of the TA/EGaIn-LM composite exhibited conductivity in the range of 0.29-1.6 MS m −1 [58]. The above fabricated systems have great potential for flexible biosensor and bielectronics applications.…”

Functional liquid metal nanoparticles: synthesis and applications

“…A recent study addresses this limitation by functionalizing natural polyphenols such as tannic acid (TA) on the interface of EGaIn to enable better adhesion of nanoparticles with diverse rigid and soft surfaces. 54 This improvement is contributed to TA molecules having universal surface adhesion property and possessing the functional groups to anchor strongly on Ga-based…”

“…This feature enables LM 4 nanoparticle ink to form high resolution conductive traces printed using different additive manufacturing techniques (i.e., inkjet printing, nozzle dispensing, ballpoint writing) for stretchable and reconfigurable interconnections. 29,[51][52][53][54][55] Despite this, the rigid and insulative oxide interface of LM nanoparticles pose a challenge to create conductive traces. [56][57][58] Several techniques ranging from mechanical, 51,52,59 thermal, 60 and laser-based [61][62][63] activations exist for coalescing the LM nanoparticles.…”