Anisotropic spin-crossover composite actuators displaying pre-programmed movements

In this work, we propose shape-morphing electro-thermal actuators, which can realize various pre-programmed movements, such as large-strain bending or helical curling. The bimorph actuators consist of an electrically conducting polymer composite layer, used for Joule heating, and a spin-crossover polymer composite layer, which affords for a large thermal strain. By using needle-shaped spin crossover particles and adjusting their orientation with respect to the two axes of the T-shaped actuator, the deformation of each device can be encoded in a predictable manner. Based on mechanical property measurements and associated finite element analysis we show that the observed movements are governed primarily by the anisotropy of the transformation strain generated by the spin crossover particles. We envision that this type of self-folding structures can be advantageously used in remote and small-scale mechanical applications.