Deterministic Role of Carbon Nanotube-Substrate Coupling for Ultrahigh Actuation in Bi-layer Electro-Thermal Actuators.

Here, actuation response of an architectured electro-thermal actuator comprising a single layer of carbon nanotube (CNT) film and a relatively thicker film of silk, cellulose or poly-di-methyl siloxane is studied. In all samples, an electric current is passed through the CNT film, which generates heat responsible for electro-thermal actuation under doubly-clamped beam configuration. All samples, including pure CNT film, show remarkable actuation, such that actuation monotonically increases with the applied voltage. Cyclic electrical loading shows a lag in the electric current stimulus and the actuation. Remarkably, an ultrahigh actuation of ~ 28 %, which was 72 times more than pure CNT film, is measured in the CNT-cellulose film, i.e., the architectured actuator with the natural polymer having functional property of hygro-expansion and structural hierarchy of CNT film, however, at significantly larger length scale. Overall, the synergetic contribution of the individual layers in these bilayered actuators enabled achieving ultrahigh electro-thermal actuation compared to the homogeneous, synthetic polymer-based devices. A detailed discussion, that also includes the role of hierarchical sub-structure and the functional properties of the substrate and numerical analysis using finite element method, is presented to highlight the actuation mechanism in the fabricated actuators.