Liquid Metal Supercooling for Low-Temperature Thermoelectric Wearables

Elastomers embedded with droplets of liquid metal (LM) alloy represent an emerging class of soft multifunctional composites that have potentially transformative impact in wearable electronics, biocompatible machines, and soft robotics. However, for these applications it is crucial for LM alloys to remain liquid during the entire service temperature range in order to maintain high mechanical compliance throughout the duration of operation. Here, LM-based functional composites that do not freeze and remain soft and stretchable at extremely low temperatures are introduced. It is shown that the confinement of LM droplets to micro-/nanometer length scales significantly suppresses their freezing temperature (down to -84.1 from -5.9 degrees C) and melting point (down to -25.6 from +17.8 degrees C) independent of the choice of matrix material and processing conditions. Such a supercooling effect allows the LM inclusions to preserve their fluidic nature at low temperatures and stretch with the surrounding polymer matrix without introducing significant mechanical resistance. These results indicate that LM composites with highly stabilized droplets can operate over a wide temperature range and open up new possibilities for these emerging materials, which are demonstrated with self-powered wearable thermoelectric devices for bio-sensing and personal health monitoring at low temperatures.