Ultrafast Photothermal Actuators with a Large Helical Curvature Based on Ultrathin GO and Biaxially Oriented PE Films.

In nature, there are some amazing superfast actuations (Venus flytrap) and large-curvature helical deformations (the awn of Erodium ). Although many bionic actuators have been made (electrothermal, hygroscopic, photoinduced), most of their actuations are slow and small, not comparable to the wonderful ones in nature. Here, we report an ultrafast photothermal actuator with large-curvature curling based on an ultrathin graphene oxide (GO) and biaxially oriented polyethylene (BOPE) bilayer film (thickness ∼11 μm). By virtue of the fast temperature changing rate (peak: 900 °C s -1 during infrared heating and -1200 °C s -1 during cooling) and the great difference in the coefficient of thermal expansion of GO and BOPE layers, the actuator deforms rapidly and greatly. The maximum bending speed and curvature can reach 5300° s -1 and 22 cm -1 , respectively, which are comparable to those of wonderful natural actuators and far exceed the performances of the reported artificial actuators. Different from ordinary helical actuators made of uniaxial anisotropic materials, our actuator is based on a typical biaxial anisotropic material of BOPE. However, the morphing behaviors of this type of actuator have not been reported before. So for the first time, we systematically studied this problem through experiments and simulations using the GO-BOPE actuator as a prototype and have drawn clear conclusions. In addition, functional GO-BOPE actuators capable of winding around and manipulating tiny objects were also designed and developed. We think this ultrafast large-curvature photothermal actuator will have wide application prospects in bionic actuations and dexterous robots.