Fig. 4
PFSA-based helical actuation. a Plots showing the bending curvature for the 20 × 60 mm bilayer actuator depending on the ratio of the active-to-inner layer thickness. b FEA results of stress distribution associated with the bending actuation of bilayer actuator. c The scheme illustrating the preparation of the three-dimensional helical buckling with an active PFSA layer line. Photos and schematic illustration of the right-handed and left-handed deformation of the composite strips with an α of 45° and 135°. SEM images of aligned PFSA lines. (Scale bar is 400 µm). d, e Schematic illustration, photographs, and time-dependent untwisting actuation of the helical strip before and after triggering by moisture
