UCLA

Dielectric elastomers (DEs) can generate large deformations in response to electric stimuli. A DE film sandwiched between a pair of compliant electrodes behaves as a deformable capacitor. The electrostatic force under an electric field causes the film to shrink in thickness and expand in area. The dielectric elastomer actuator (DEA) technology is superior to most other electrical actuation technologies regarding its large actuation strain, high energy density, light weight, mechanical compliancy, and low cost. However, it has been challenging to transition the DEA technology into practical products due to its low operational stability caused by material limitations (DEs and compliant electrodes) and lack of suitable multilayer fabrication processes. Carbon nanotubes (CNTs) have been widely used as compliant electrodes for DEAs. However, the sharp tips of CNTs induce corona discharges in air under high electric fields, eventually leading to dielectric breakdown. One focus of this dissertation is on developing a CNT-related compliant electrode with long-term stability and reliability at large strains. A bilayer electrode consisting of an ultra-thin CNT network overcoated by a thin polymer layer is introduced. The thin polymer layer serves as the dielectric barrier to suppress corona discharges of the nanotubes in air. The bilayer electrode is compliant and maintains its conductivity under large deformation. The self-clearing property of this bilayer electrode affords fault tolerance; corona discharge that could potentially leads to dielectric breakdown of the DEA is transformed into small current spikes. With the bilayer electrode, the operation stability of VHB acrylic elastomer-based DEAs is improved to 1000 cycles at 150% area strain under a square-wave voltage and 5.5-hours continuous actuation at a constant voltage. The VHB acrylic elastomer is a commonly used DE material due to its ability to sustain high electric fields and reach large actuation strains and energy densities. However, high prestrain is required to obtain the high performance. The frames used to support the prestrain limit device flexibility, reduce overall specific energy density, and cause fatigue over time. Therefore, another focus of this dissertation is to synthesize high-performance prestrain-locked VHB DEs. The prestrain-locked free-standing DE films, VHB-IPN-Ps, have lower viscoelasticity and Young’s modulus as compared to highly prestrained VHB films. VHB-IPN-Ps respond to electric fields fast and reach large strains at relatively low electric fields. The DEA based on the VHB-IPN-P and the bilayer electrode can be operated over 5000 cycles at strains above 80% under a square-wave voltage stably and reliably. A multilayer stacking process based on VHB-IPN-Ps and the bilayer electrodes is also developed. This process is a hybrid of wet deposition and solid film lamination and has the potential to be scaled up for the manufacturing of multilayer DEAs. This dissertation also studies a DE derivative material, a phase-changing bistable electroactive polymer (BSEP), to enable rigid-to-rigid actuation without complex structures. Unlike most BSEPs, which have broad glass transition temperature bands over 30 �C to complete the modulus change, the phase-changing BSEP undergoes reversible melting-crystallization of the polymer chains in a narrow temperature band, resulting in a modulus change within 10 �C. A tactile display of Braille standard resolution was explored based on the phase-changing BSEP. It employed ‘Prestretch-Pattern-Protect-Release’ to pattern the serpentine electrode for Joule heating to administer the phase change under a pneumatic actuation mechanism to deform the polymer at the softened state. This work has improved the phase-changing BSEP to achieve over 1000-folds modulus change within 3 �C. A laser-engraving process is adopted to pattern the serpentine electrode for localized Joule heating with high resolution. The resulting tactile display achieves large vertical displacements of the Braille dots and high blocking forces under a low power supply. This tactile display may potentially be made user-safe and cost-effective in various tactile-display-related devices.