An actuator generally requires low-voltage actuation, high displacement, and high responsiveness. However, no polymer actuator meets all these requirements. Because nanofibers have a diameter of 1 μm or less and a large specific surface area, physicochemical energy change is expected to affect the driving process. We expected polymer nanofibers to meet these requirements owing to the shape effect of nanofibers. Previously, we successfully drove a polyurethane/FeCl3 composite nanofiber as an actuator by applying voltage. FeCl3 was used as a conductive filler. However, the mechanism of driving was not revealed. In this paper, we report the driving behavior of a nanofiber actuator. We considered thermal expansion by the joule heating of nanofibers as the mechanism of actuation in polymer nanofiber. For investigating the effect of joule heating on a nanofiber, we employed a multilateral approach. First, we compared the driving of nanofibers made of two types of polymers with different coefficients of thermal expansion. Next, we investigated the effect of temperature change and the nanofiber diameter on driving. The results suggest that the nanofiber actuator was driven by thermal expansion with a temperature change of 33 °C at an applied voltage of 50 V. Finally, we improved the nanofiber heat transfer by fabricating a poly (ethylene co vinyl acetate)/carbon nanotube composite nanofiber. We successfully improved driving displacement by introducing carbon nanotubes into the nanofibers.
