Fabrication of Stretchable, Self-Healable, and Water-Resistant Electronic Devices Based on Dynamic Covalent Bonding Polyurethane

There has been extensive research on self-healing electronics to extend their lifespan in accordance with a recent interest in environmental issues. As self-healing materials for soft devices, hydrogels have been most widely used, but there are intrinsic demerits of easy loss of mechanical and self-healing properties due to evaporation of water under ambient conditions. Non-hydrogels used as an alternative to hydrogels, however, show low self-healing efficiency or uncontrolled self-healing, limiting its practical application.<br/>Here, we report a fabrication of self-healing electronic devices based on a dynamic covalent bonding polyurethane (PU) consisting of poly(dimethylsiloxane) and poly(tetramethylene glycol) as a soft segment, isophorone diisocyanate as a hard segment, and dynamic oxime-carbamate bond that is reversible at 60 °C. The polymer contains both urethane and urea bond so that its mechanical properties are improved because their strength of hydrogen bonding are different. As a result, the synthesized PU can be stretched up to 1100 % and its tensile strength at break is 0.94 kPa. It also exhibits a superior self-healing ability, recovering 93.7 % of its mechanical property after contact at 65 °C for 6 h where undesired restoration is prohibited via introducing reversible covalent bonding only at the specific temperature. Furthermore, water contact angle of the polymer is 100 °, having hydrophobicity and self-healing in water is also possible. Based on the self-healing polymer, we fabricated a wirelessly powered self-healing sensor devices. Via use of Galinstan liquid metal interconnection, the whole sensor device including the antenna shows a stable operation even after self-healing from the mechanical bisection. This work demonstrates a great potential application of our synthesized dynamic covalent bonding polyurethane to various long lifespan wearable devices which are deformable and stretchable as well as self-healable.