Liquid Metal/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Composite Hydrogels with Multi-Stage Gauge Factors, Pressure Resistance, and Wide pH Stability

Liquid metals are highly desirable in various applications such as electronic skin, soft sensors, and flexible electrodes due to their ultrahigh conductivity and exceptional fluidity. However, their practical utility is hindered by challenges related to the high surface tension and susceptibility to oxidation, leading to poor wettability on hydrophilic substrates. In this study, we present an approach to significantly improve the surface wettability of liquid metals on hydrogels, facilitated by poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Through strong polymer chain entanglements, PEDOT:PSS is capable of adsorbing onto the surface of prestretched hydrogels, thereby providing a robust infiltration substrate for liquid metals. Even when immersed in an aqueous solution with a pH of 4–7, liquid metals can be firmly adhered to the PEDOT:PSS surface for up to 30 days. The remarkable infiltration capability of PEDOT:PSS, combined with liquid metals, enables the formation of continuous and stable conductive pathways on the hydrogel surfaces. The resulting conductive hydrogels exhibit different sensitivity factors in three different stretch ratio ranges for various applications in soft electronic systems. This PEDOT:PSS-assisted approach holds promise for applications in soft circuits, sensors, and flexible electronics, thus offering significant potential for wearable sensor technologies.