Three-layer ionic polymer–metal composite actuator with functionalized carbon nanotubes incorporated into Nafion

Ionic polymer–metal composite (IPMC) actuators are a type of soft actuators. They can be controlled with low voltages and produce large curvatures. Capacitance is a parameter that determines the performance of an IPMC actuator. To increase the capacitance of an IPMC, we mixed functionalized carbon nanotubes (CNTs) in a Nafion layer. High-surface-area CNTs can increase the surface area of electrodes, and thus increase the capacitance. We found that Au–CNT networks are formed inside the Nafion layer by reduction of Au during electrode preparation when the functionalized CNTs were completely dispersed in Nafion. We fabricated three-layer IPMC actuators with a pure Nafion layer sandwiched between outer layers of the CNT–Nafion mixed polymer to use this Au–CNT effectively. By applying a square and sinusoidal wave voltage, we compared the performance of the three-layer IPMC actuator with that of a conventional IPMC actuator. The capacitance of three-layer IPMC actuator was 2.2 times larger than that of the conventional IPMC actuator. The displacement of the three-layer IPMC actuator was 1.3–2.3 times larger than that of the conventional IPMC actuator at slower than 1.0 Hz voltage wave applying.