Stable and High‐Strain Dielectric Elastomer Actuators Based on a Carbon Nanotube‐Polymer Bilayer Electrode

Abstract

Dielectric elastomer actuators (DEAs) have shown promises in numerous applications such as bio‐inspired robotics, tactile displays, tunable optics, and microfluidics, owing to their unique combination of large actuation strain, high energy density, and light weight. However, the practical applications of the DEAs have been hindered partly due to their poor reliability and durability under high‐strain actuation. A major failure mechanism is from the localized electrical breakdown. Compliant electrodes with self‐clearing capability have been studied to prevent premature failures. Here, an interpenetrating bilayer compliant electrode comprising a thin layer of a water‐based polyurethane (WPU) overcoated on an ultrathin single‐walled carbon nanotube (SWNT) layer is reported. The thin polyurethane layer serves as the dielectric barrier to suppress corona discharges of the nanotubes in air. The SWNT+WPU bilayer electrode has the capability to self‐clear at the breakdown sites, enhancing the fault tolerance and mendability of the DEA at a large‐strain actuation. Stable actuation at 150% area strain for 1000 cycles under square‐wave voltage and 5.5‐h continuous actuation at a constant voltage have been achieved for acrylic elastomer‐based DEAs.

Soft Actuator Materials for Electrically Driven Haptic Interfaces

“…[ 107 ] Other material matrices such as styrene ethylene butylene styrene (SEBS) block copolymer, polyurethanes, and styrene rubber have also been utilized for DEAs but have provided limited success in terms of improving the mechanical performance. [ 107,117,118 ]…”

“…Pei et al reported the use of the interpenetrating SWCNT–polyurethane bilayer electrode, where the water‐based polyurethane acted as a protective overlayer to CNT against terminal failure due to corona discharge in air, with negligible effect on self‐clearing, conductivity, and actuation, enabling stable, continuous actuation (5.5 h) at constant voltage and 150% area strain for 1000 cycles. [ 257 ] Nanowire–polymer composite systems are also widely used as compliant electrodes. [ 8,258–260 ] One of the earlier demonstrations for actuators was utilizing a silver nanowire–polymer composite, consisting of an ultrathin layer of silver nanowire in a poly( tert ‐butylacrylate‐ co ‐acrylic acid) poly(TBA‐co‐AA) layer, where the electrode retained electrical conductivity at 140% strain albeit with a resistance increase of 10−100 times.…”

Solvent‐Free Synthesis and Processing of Conductive Elastomer Composites for Green Dielectric Elastomer Transducers

“…[15][16][17][18][19][20][21][22][23] Although CNTs and metal nanowires (NWs) provide great conductivity, compliance, stability under high voltages, and may selfclear, these materials are not without drawbacks. [24][25][26] The former is cancerogenic, while the latter is rather expensive and needs large amounts of solvents for its synthesis. [27,28] Doped conductive polymers such as poly(3-dodecyloxylthiophene) and polyaniline showed promising conductivity.…”

“…[2,12,31] Peng et al used single-wall carbon nanotubes (SWCNT) electrodes and obtained self-clearable electrodes with a sheet resistance of 100 kΩ sq −1 and good stability over one thousand cycles at an areal actuation strain of 150%. [25] Quinsaat et al used a mixture of carbon black and graphene nanoparticles (GNPs) dispersed in a PDMS and achieved an electrode material with a conductivity of 7.8 S cm -1 and contact resistance of 5 Ω. [32] The electrode was processed by screen-printing, which was facilitated by adjusting the viscosity of the composite by solvent.…”

Property enhancement in flexible poly(vinylidene fluoride)‐based piezoelectric films with large‐area preparation

“…Flexible and stretchable electronics are widely used in wearable sensors, energy harvesters, and other fields 1–5 . For example, poly(vinylidene fluoride) (PVDF) also with its copolymers can be used for preparing flexible piezoelectric sensors and actuators 6–11 for they have superior mechanical properties, chemical resistance, and piezoelectricity 12–17 .…”