Recyclable Liquid Metal‐Based Circuit on Paper

Abstract

and touch panel. [18] As people expected, [17] the processability, performance, and stability of electronic materials are basic characteristics of paper electronics which demand that paper-based circuits must have controllable scale, low resistance and high stability under deformation. Although most paper electronics are disposable, the circuits on paper will also raise environmental concern as they cannot be degraded or recycled like their substrate paper. [19] Burning is the popular method to recycle functional materials such as silver nanoparticles on paper, [1,20,21] it will be detrimental to environment and functional materials which are also difficult to be separated from the debris of paper. Therefore, an environmentally friendly method for fabricating and recycling of paper-based circuits is urgently needed. Basically, all paper electronic devices contain functional modules and circuits. The circuit with controllable scale and high folding stability is the key point on deciding the integration level of devices and electrical stability under deformation. Recently, the fabrication of flexible circuits on paper is mostly based on the connection of tiny conductors, such as metal nanoparticles, [3,7,9,18,22,23] metal nanowires, [15,24] and graphene. [16] Alternatively, conductive liquids (especially liquid metals) were expected to realize circuits with high folding stability for intrinsically combined characteristics of both high electrical conductivity and excellent fluidity. [25] Liquid metal (LM, Galinstan: 68.2 wt% Ga, 21.8 wt% In, 10 wt% Sn [26] ) exhibits favorable properties such as low melting point, [27] high electrical conductivity, [28] and low toxicity. [29] LM has been patterned on a variety of smooth substrates such as polydimethylsiloxane and polyvinyl chloride [25,26,[30][31][32][33][34][35][36][37] to function as circuits, sensors, and antennas. [25,31,32,[37][38][39] However, impeded by the porous topography of paper, it is hard to reduce the line-width of paper based LM circuits thinner than 200 µm with methods like direct writing, [40] desktop printing, [37,41] and screen printing. [42] With the LM, here the method for fabricating circuits with controllable line-width and high stability is demonstrated, and these circuits can be recycled based on the transforming mechanism between different morphologies of LM (bulk, wires, and microparticles). Bulk LM can be deformed into LM particles (LMPs) by sonication. [43] Then, LMPs can be deposited on paper which can further be selectively transformed into LM wires through mechanically sintering. [38,44] Two strategies were introduced in the mechanically sintering process to control the width of circuit (pristine circuit) by controlling the contact Paper electronics is considered very environmentally friendly, but effective recyclability of metallic circuits on paper still needs more improvement. Therefore, liquid metal (Galinstan) circuits based on the reversible conversion from particles to wires are fabricated on paper using mechanical methods, i....

Liquid Metal‐Based Transient Circuits for Flexible and Recyclable Electronics

“…In the experiment, about 96% of the liquid metal can be recovered by this method, while 4% of the RTLM are resorbed during oxide‐layer removal. Such a retrieval rate obtained by our strategy is significantly higher than the rate obtained by the strategy of Li et al, who utilized ethanol and ultrasonication to retrieve up to 91% of the RTLM from paper electronics . The recycled liquid metal can be reused for the fabrication of new circuits or other applications.…”

“…The CNTs were dispersed during dissolution of the support, rendering the recovery challenging. RTLMs, however, are readily recycled, which have been reported in some early recycling attempts of RTLMs by us and other groups . Similarly, the as‐made RTLM‐based transient devices can be recycled.…”

Smart Textile‐Integrated Microelectronic Systems for Wearable Applications

“…A previous review covered conductive materials like PEDOT:PSS, CNTs, graphene, and metals for paper electronics. Recently, liquid metals (LM) were used to fabricate circuit on paper due to their both superior electrical conductivity and high fluidity . Guo, e.g., developed a paper‐based circuit through one‐step LM transfer printing method .…”

High-Adhesive Flexible Electrodes and Their Manufacture: A Review

“…Due to the fluidity, high surface tension, and easy oxidation characteristics of LMs, there are certain challenges to realize its patterning [35]. In addition, the high cost of LM also restricts its applications, and researchers have recently studied the recycling of LM to broaden its scope [75].…”