Deterministic Role of Carbon Nanotube-Substrate Coupling for Ultrahigh Actuation in Bilayer Electrothermal Actuators

Here, the actuation response of an
architectured electrothermal
actuator comprising a single layer of carbon nanotube (CNT) film and
a relatively thicker film of silk, cellulose, or polydimethylsiloxane
is studied. An electric current is passed through the CNT film, which
generates heat responsible for electrothermal actuation, in all samples,
affixed as per doubly clamped beam configuration. All samples, including
pure CNT film, show remarkable actuation such that actuation monotonically
increases with the applied voltage. Cyclic pulsed electrical loading
shows a lag in the electric current stimulus and the actuation. Remarkably,
an ultrahigh actuation of ∼2.8%, which was 72 times more than
that shown by pure CNT film, is measured in the CNT–cellulose
film, that is, the architectured actuator with the natural polymer
having the functional property of hygroexpansion and the structural
hierarchy of the CNT film, however, at a significantly larger length
scale. Overall, the synergetic contribution of the individual layers
in these bilayered actuators enabled achieving ultrahigh electrothermal
actuation compared to the homogeneous, synthetic polymer-based devices.
A detailed discussion, which also includes examination of the role
of the hierarchical substructure and the functional properties of
the substrate and numerical analysis using the finite element method,
is presented to highlight the actuation mechanism in the fabricated
actuators.