Spraying printing of liquid metal electronics on various clothes to compose wearable functional device

Liquid metal printing is emerging as an important tool for making wearable electronics. However, very limited academic efforts were made to fulfill such an increasing need. This paper is dedicated to present relatively complete theoretical and experimental characterizations for liquid metal spraying printing towards developing wearable electronic textile. The practical conditions of liquid metal droplets in the spraying printing process such as the jet velocity, the size distribution of droplets and their evenness degree, the morphology of droplets and their unrolling areas after impacting the substrate are quantified. The dominating factors, including the oxidation of liquid metal and the pressure force on cloth substrate during the impacting process, which ensure liquid metal firmly adhere to the cloth, are clarified. Further, various clothes are comparatively investigated to test their capabilities in printing liquid metal conductors, where the resistance difference can be over thousand-fold. In addition to interpreting the basic mechanisms and performances of the spraying printing, two programmable flexible circuits with specifically designed functions such as blinking LED lighting and wireless infrared temperature measurement via current manufacture technology were also demonstrated and evaluated for their washable ability. With the realization of wearable modules via liquid metal printing technology, it can be expected that flexible functional devices on cloth fabricated quickly and directly would witness more broad applications in the coming time.