Anisotropy behavior of liquid metal elastomer composites with both enhanced thermal conductivity and crack resistance by direct ink writing

Liquid metal elastomer composites (LMEC) have broad application prospects in flexible devices, but the research on the basic processes of DIW for LMEC and the properties of DIW-ed LMEC is lacking. In this study, liquid metal (LM) is added to silicone elastomers such as Polydimethylsiloxane (PDMS), and the effect of LM volume fraction on ink rheology is investigated. Results show that the storage modulus of ink is lower than its loss modulus, which is not conducive to self-support formation. Therefore, fluorination is adopted to treat the silicon dioxide substrate used, thereby reducing the deformation rate of the printed structure to below 110%. The results of properties show that the crack resistance and thermal conductivity of soft elastomers increase with the LM volume fraction. Additionally, the tensile properties of PDMS printed via DIW exhibit significant anisotropy parallel and perpendicular to the scanning direction, and that the addition of LM droplets reduces the anisotropy. And with the increase of curing temperature and LM droplet size, the stretchability of DIW-ed LMEC in both directions decreases, but only LMEC samples cured at 140℃ exhibit significant anisotropy. This study provides guidance pertaining to the basic process and printing directions for the application of DIW in the manufacture of LMEC equipment.