Shape programming of polymeric based electrothermal actuator (ETA) via artificially induced stress relaxation

Electrothermal actuators (ETAs) are a new generation of active materials that can produce different motions from thermal expansion induced by Joule heating. It is well-known that the degree of deformation is determined by the amount of Joule heating and the coefficient of thermal expansion (CTE) of the material. Previous works on polymeric ETAs are strongly focused on increasing electrical conductivity by utilizing super-aligned carbon nanotube (CNT) sheets. This allows greater deformation for the same drive voltage. Despite these accomplishments with low-voltage actuation, many of the ETAs were constructed to have basic geometries such as a simple cantilever shape. In this paper, it was discovered that shape of polymeric ETA can be programmed into a desired configuration by applying an induced stress relaxation mechanism and post secondary curing. By utilizing such effects, an ETA can be programmed into a curled resting state which allows the actuator to achieve an active bending angle over 540°, a value far greater than any previous studies. This shape programming feature also allows for tailoring the actuator configuration to a specific application. This is demonstrated here by fabricating a small crawling soft robot similar to mimic an inchworm motion.