Behavior of polymer-based electroactive actuator incorporated with mild hydrothermally treated CNTs

Abstract

We fabricated an actuator that was made from polyurethane (PU) with carbon nanotubes (CNTs) as the filler. To improve the dispersion of the CNTs, a mild hydrothermal treatment was carried out. Carboxyl and hydroxyl groups were introduced to the surface of the CNTs, and they were found to be highly dispersed in polar solvents such as dimethylformamide. To evaluate these films, we mainly focused on electrical properties, such as dielectric spectroscopy, space charge measurements, and actuator behavior. We found that the PU/CNTs film bents toward the cathode when an electric field was applied, and it reverted to its original position when the electric field was removed. Upon the inclusion of the CNTs as the filler for the polymer, the electrical properties of the films improved significantly. The highly polarized films had a high relative permittivity, and this produced a higher Maxwell pressure, which assisted the actuation. A high accumulated charge density was observed from space charge measurements in some of the films, and this explains the bending direction and the actuation mechanism.

Bending actuation and charge distribution behavior of polyurethane/carbon nanotube electroactive nanocomposites

“…b, similar bending deformation can be observed in each voltage cycle. This phenomenon can be considered to be a type of memory where the electric field reminds the films of the electrically memorized strain, which also indicates that the actuation is reproducible and stable upon voltage cycling . Furthermore, the recovery after the application of voltage for PU/CNTs 0.5 wt% was lower than PU/CNTs 1.0 wt%.…”

“…Carboxyl and hydroxyl functional groups of the modified CNTs led to well‐dispersed PU/CNT films. The introduction of functional groups to the CNTs allows covalent bonding of PU directly to the nanotube framework and significantly improves the interface between the PU and the modified CNTs . Microwave‐induced polymerization treatment thus improves the dispersion of pristine CNTs.…”

“…However, not only heat, stimulations such as electric fields will enable the manipulation of shape memory behavior at ambient temperature and eliminate the temperature constraints arising from external heating . An electric field‐stimulated polymer‐based actuators are referred to as electroactive polymers (EAPs) and can be considered as a type of SMP . They are soft and flexible materials that can convert electrical energy to mechanical energy and thus impart a force and produce large strain .…”

“…An electric field‐stimulated polymer‐based actuators are referred to as electroactive polymers (EAPs) and can be considered as a type of SMP . They are soft and flexible materials that can convert electrical energy to mechanical energy and thus impart a force and produce large strain . They can be applied for actuator materials, sensors, artificial muscles, smart devices, and microswitches .…”

“…Generally, polyurethane (PU) are insulators and they are light, soft, flexible, easy to fabricate, and have been reported to generate deformation and large strain under electric field stimulation . Meanwhile, carbon nanotubes (CNTs) are also light, possess a high aspect ratio, and have outstanding mechanical, chemical, and electric properties . Upon combining a polymer (PU) with an electric conductor (CNTs) as a filler, new and unique polymer‐based nanocomposites can be fabricated.…”