Self-sintering liquid metal ink with LAPONITE® for flexible electronics

Abstract

Liquid-metal (LM)-based flexible and stretchable electronics has attracted widespread attention in soft robotics, self- powered devices and electronic skins. Although nanometerization can facilitate the deposition and patterning of LMs onto substrates, subsequent mechanical or laser sintering operations must be employed to recover their conductivity, which limits their wider standardized applications. To address this critical challenge, a novel self-sintering technique to prepare thin conductive patterns by employing a special LM-LAPONITE (R) (LML) ink is presented, which utilizes the capillary force between nanoparticles to sinter LM droplets and therefore requires no subsequent sintering operations. The LML ink is prepared by sonicating the mixture of bulk LM and LAPONITE (R) aqueous dispersion and possesses excellent fluidity. A theoretical model based on surface tension is established to explain the spontaneous sintering process and the effect of forces on LM droplets. In contrast to conventional passive sintering strategies, this self-sintering strategy is substrate-friendly and available to more types of substrates, including both rigid and soft substrates, and even fragile materials like leaves. Furthermore, several typical flexible electronic devices including near-field communication (NFC) tags, leaf circuits and data gloves are fabricated and investigated to demonstrate the capability of this strategy for directly manufacturing LM-based flexible electronic devices.