Fabrication of spin crossover nanocomposites and devices for electromechanical applications

In order to synergistically exploit the volume change of spin crossover (SCO) materials, polymeric SCO composite materials were fabricated thanks to molecular engineering and nanosciences. These materials were conceived with two applications in mind: thermal energy harvesting and artificial muscles. Regarding thermal energy harvesting applications, a series of SCO@P(VDF-TrFE) composites were elaborated. The volume change of the spin crossover phenomenon activates the piezoelectric P(VDF-TrFE) copolymer matrix when thermally stimulated. This leads to a current discharge at the spin transition temperatures, showing a synergistic effect between the piezoelectric polymer matrix and the SCO filler material. These materials can thus be used to recover electrical energy from small thermal excursions around the spin transition temperature. Regarding the fabrication of materials for the development of artificial muscles, a bilayer approach was used to amplify the effect of the volume change associated with the SCO phenomenon. Two different strategies were used to obtain these bilayer materials: 3D printing and solvent casting. 3D printing techniques allowed for the reproducible fabrication of SCO printed composites with very high control over their morphology, allowing us to obtain geometries never before seen for this kind of materials. Thermally activated bilayer actuators were successfully fabricated and their mechanical properties proved competitive with other materials in the field. Solvent casting techniques allowed us to obtain electrically conductive SCO bilayer actuators. These actuators were optimized via smart material design by the inclusion of aligned anisotropic spin crossover nanoobjects. These devices, electrically activated via Joule effect, are highly controllable, and closed-loop operation showed that they are highly resilient, robust, precise and efficient. A gripper demonstrator device was thus fabricated, showing the applicability of these materials in robotic devices. Finally, we successfully fabricated composite materials which exploit the volume change of the SCO phenomenon and which have applicability in electromechanical devices.