Controllable and Facile Metallization of Polymer Surface with Biphasic Liquid Metals toward Soft Circuits

Chemical metallization (e.g., chemical/electrical plating) of the polymer surface is an extremely important, convenient, cost-effective, and broadly applied strategy to realize combined advantages of functional metals and polymers for today's industry. However, traditional chemical and electrical metallization of polymer surfaces requires the participation of physical methods, which greatly constrains the utilization of versatile metals in modern electronics. This work successfully utilized a traditional chemical strategy to address the challenging preliminary conductivity and subsequent liquid metal (LM) metallization of insulated polymer surfaces. Through the facile strategy, an ultrathin (6 μm) LM film could be conveniently coated on both the external and internal surface of polymers to fabricate large-area flexible circuits with fine line width (15 μm) at low-cost (9.5 $·dm^-2). A detailed reaction mechanism of the LMs was reported, and various chemical parameters of the metallization were thoroughly investigated. Interestingly, the metallized polymer surface showed a distinguished CuGa₂/Ga biphasic structure of the LMs, which enabled the polymer as an extraordinarily soft conductor with ultrahigh uniaxial strain (>1200%), extremely low resistance variation (R/R < 7), strong metal-polymer adhesion (1.5 N·mm^-1), and excellent electrical durability. Furthermore, with the benefit of the photolithography technique, precisely designed circuits could be achieved, and wireless transmission/control soft electronic devices were easily fabricated.