Printable, Stretchable Liquid Metal Conductors Based on EGaIn-Ecoflex Composites

Abstract

Liquid metal elastomer composite (LMEC) brings unique advantages for soft and stretchable electronics by patterning flexible electrical circuitry. By incorporating 3D printing technology, seamless design configuration with high manufacturability of stretchable electronics can be achieved. However, the option of elastomers is greatly limited by the immediate surface oxidation of liquid metal (LM) particles. When we try to increase the stretchability of liquid metal elastomer composite (LMEC) by using ultra-soft elastomers, the failure to conduct electricity often occurs. In addition, tiny LM particles (1-5 microns) have better printing performance and also cause LMEC not to be conductive. Therefore, it is extremely challenging to use both highly stretchable soft elastomers (such as Ecoflex 00-30) and small-sized LM particles to make stretchable conductors.In this study, we address three key scientific questions about liquid metal composites and their electromechanical response. Firstly, we investigate the successful synthesis of conductive LMEC from highly stretchable silicone elastomers with particle sizes approaching 1 micron. Secondly, we examine whether the LM microparticles experience an increase in size when dispersed in an elastomer. Lastly, we explore the relationship between the electromechanical response of LM-based conductors and the rate of applied deformation. These questions and hypotheses serve as the foundation for our research and provide valuable insights into the behavior of LMEC in various conditions. The results show the printed composites show excellent electrical and electromechanical properties, such as an electrical resistance of 0.2 Ω/cm at unload, a low resistance variation up to 700% strain. The robustness of LMEC was also tested for 1000 cycles at 300% uniaxial tensile strain and 5000 cycles at 200% uniaxial tensile strain. Additionally, the LMEC exhibited an extremely low resistance variation even under high-speed displacement, highlighting its potential for applications in stretchable and wearable electronics. These findings highlights the promising capabilities of LMEC in various practical applications.