A highly porous nafion membrane templated from polyoxometalates-based supramolecule composite for ion-exchange polymer-metal composite actuator

Abstract

This paper reports a new technique for fabricating a highly porous hybrid SiO2/Nafion membrane, from which a high electromechanical performance ion-exchange polymer-metal composite (IPMC) actuator is achieved. This technique uses polyoxometalate (POM)-based supramolecule composite carried by amorphous SiO2 particles to form a hybrid membrane with the polar Nafion ionomer. The resultant composite (POM-Nafion) is then incubated and degraded in a base solution, forming a porous membrane. Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM) were used to monitor the degradation process. ATR-FTIR results demonstrated that the POM-based composite was removed while SiO2 remained in the porous membrane after degradation. SEM images showed that there were a great quantity of channels with sizes of 0.4–1.4 μm and pores with sizes of 300–700 nm in the newly-formed porous Si-Nafion membrane. With the same Nafion content, the porous Si-Nafion membrane and self-casting Nafion membrane were both made into IPMC actuators. A laser displacement sensor, a force sensor and a high speed camera were assembled into a measurement system to evaluate the performance of the IPMC actuator. Results showed that the maximum blocking forces from the Si-Nafion membrane actuator were 3.78 g for 2.5 V driving voltage and 2.39 g for 1.5 V, which increase by 2.97 and 4.19 times, respectively, when compared to the self-casting Nafion membrane actuator. The maximum displacement outputs were 7.2 mm for 2.5 V driving voltage and 5.9 mm for 1.5 V. Compared to the self-casting Nafion membrane actuator, these outputs increased by 4.8 and 9.7 times, respectively. When actuated in the air, the Si-Nafion membrane actuator exhibited stable working time of 480 s and 710 s for the voltages of 2.5 V and 1.5 V, respectively. Compared to the self-casting Nafion membrane actuator, these data increased by 4.36 and 2.22 times, respectively.