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provide flexibility and high anisotropic properties and are capable of very complex actuation behavior. [5,6] Tensile and torsional actuations can be realized in fibers when subjected to a constant external stress, while fibers also need to be programmed by twisting or coiling in a post manufacturing process. [7-9] Free-standing reversible actuators are required for applications, where a reversible muscle-like movement should be realized-by only a single actuator. As shape-memory polymer actuators [10] or shape-memory composite fibers [11] are typically thermally controlled, their applicability in robotic applications would benefit, if they could be electrically actuated. Here we aim at shape-memory polymer fibers, which are electrically actuable and could be scaled-up in a conventional manufacturing environment. Resistive heating or Joule heating, as popularly known, can be achieved in conductive polymeric systems, which is due to their resistance to the flow of current. Conductive composites as well as conductive coatings can be developed to realize joule/ resistive heating in polymers. [12-14] Metal particles, carbonbased inorganic conductive fillers or conductive polymers are used to achieve conductivity in polymeric materials for joule heating. [15-17] Heating phenomena in composites rely on incorporation of a conductive filler in the core enabling heat generation inside the core material and heat transfer to the polymer matrix. In the coating approach, the conductive material forms a shell on the fiber surface. When a certain voltage is applied, heat is generated at the surface and is transferred to the fiber core. In addition to the physical principles, some engineering principles also need to be considered. Incorporation of inorganic fillers lead to disturbance of crystallites in the polymer matrix and affect other properties related to these crystallites, such as shape-memory properties. A filler content up to 40 wt% is reported in shape-memory polymer composites. [18,19] Similarly, a coating might add stiffness to fibers, which could lead to hinder the movement of core material. In this study, we present electrically triggered fiber actuators to overcome the limitations of thermally driven actuators by transferring actuator technology to polymeric fibers and enabling joule heating to trigger actuation function at the same time. We aimed at an actuation, which can be triggered by resistive heating within a domestic voltage supply range. Our concept was to use carbon-based conductive fillers such as carbon black (CB), carbon nanotubes (CNTs) and graphene Robots are typically controlled by electrical signals. Resistive heating is an option to electrically trigger actuation in thermosensitive polymer systems. In this study electrically triggerable poly[ethylene-co-(vinyl acetate)] (PEVA)based fiber actuators are realized as composite fibers as well as polymer fibers with conductive coatings. In the coated fibers, the core consists of crosslinked PEVA (cPEVA), while the conductive coating shell is achieved v...

Abstract:Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(ε-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5-60 wt % of non-crosslinked polymer chains, which freely interpenetrate the crosslinked network, were achieved leading to differences in the resulting phase of the bulk material. This can be described as "sponge-like" with open or closed compartments depending on the amount of interpenetrating polymer. The crosslinking density and the average network chain length remained in a similar range for all network structures, while the theoretical accessible volume for reptation of the free polymer content is affected. This feature could influence or introduce new functions into the material created by thermomechanical treatment. The effect of interpenetrating PCL in cPCLs on the reversible actuation was analyzed by cyclic, uniaxial tensile tests. Here, high reversible strains of up to ∆ε = 24% showed the enhanced actuation performance of networks with a non-crosslinked PCL content of 30 wt % resulting from the crystal formation in the phase of the non-crosslinked PCL and co-crystallization with network structures. Additional functionalities are reprogrammability and self-healing capabilities for networks with high contents of extractable polymer enabling reusability and providing durable actuator materials.