A new high-performance ionic polymer–metal composite based on Nafion/polyimide blends

Abstract

For the first time, we report ion-exchange membranes based on Nafion and polyimide (PI, Kapton) blends to fabricate ionic polymer–metal composites (IPMCs). Polyamic acid [PAA, poly(pyromellitic dianhydride-co-4,4′-oxydianiline), as a precursor of PI] solution was blended with Nafion solution using physical blending method to provide PAA–Nafion blend membrane. This work demonstrates that, by simple physical blending method, the thermal and mechanical properties of Nafion can be improved while maintaining the excellent actuating performance. After thermal imidization, PAA converted into PI, resulting in PI–Nafion blend membrane. Optimum conditions to cast PAA–Nafion blends and thermal imidization have been established, and blend membranes with PI wt% of 6, 12, 18, and 30 were prepared. Fourier transform infrared spectroscopy confirmed the incorporation of PI in the Nafion matrix. Thermal decomposition unique to the PI became more noticeable as the content of PI increased, which was measured by thermogravimetric analysis. Dynamic mechanical analysis showed that the storage modulus (E′) increased as a function of PI content while loss modulus (E″) exhibited only a minor change, which resulted in the decrease in the damping properties (tan δ). The blend membranes were fabricated into IPMCs by deposition of platinum electrode onto the membrane surface through electroless plating process. Among tested, NPI-18 IPMC actuator, which has 18 wt% of PI in Nafion, showed comparable electromechanical performance to the commercially available Nafion 117 IPMC actuator.