Enhanced movement of CNT-based actuators by a three-Layered structure with controlled resistivity

Due to their unique movement and the lack of motoric parts, flexible actuators have recently been attracting considerable attention in regards to fabrication of soft robots. One of the most known flexible actuators are electro-thermal actuators (ETAs), based on Carbon Nanotubes (CNT). These are bi-layered actuators, triggered electrically, and capable of preforming actuation because of the different coefficient of thermal expansions (CTEs) of the layers. The main disadvantage of these actuators is their limited movement ability, therefore, significant efforts are being invested in improving the actuation of CNT-based actuators. A typical CNT-based actuator is composed of a CNT layer on a polyimide substrate. In this study we show how the deflection of the CNT-based actuators was improved by decreasing the resistance of the CNT layer. We also present, for the first time, a novel tri-layer structured actuator that enables extremely large movements, with a record value deflection of 300°, using a simple, low-cost fabrication method without any orientation of the layers. This was achieved by adding a third layer of a photopolymeriazble polymer on top of the two typical bilayer CNT Kapton device. We further modeled the effect of various parameters of the third layer, such as the Young's modulus and the thickness, on the actuation, supporting the experimental data.