High electromechanical response electroactive polymers and their applications for solid state actuators

This dissertation discusses the limiting factors in ionic polymer conductor network composite (IPCNC) actuators and develops solutions to overcome the barriers of low actuation speed and electromechanical efficiency. Two important components, conductor network composites (CNCs) and electrolytes, which determine performance of IPCNCs are investigated and analyzed for developing improvement solutions.;In IPCNC actuators, it is CNC layers that control actuator speed. Ion transport in traditional porous composite electrodes is slow because of long transport paths caused by both large thickness and random morphology. CNCs with thickness more than 20 microm are usually fabricated due to the limitation brought by the fabrication methods. To solve the problem, layer-by-layer (LbL) self assembly with fine thickness control ability is used to fabricate CNC layers, with ultrathin thickness (sub-micrometer). Increases in actuator speed (response time ≈0.18 s) is demonstrated with LbL CNCs. An additional improvement is also shown where strain has been increased to 6.8%, compared with traditional IPCNC or ionic polymer metal composite (IPMC) (maximum strain ≈3.3%). Also, thin CNCs have led to both high electrical and electromechanical efficiency. The importance of CNC morphology is demonstrated in IPCNC actuators, for the very first time thanks to recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fraction. Compared with traditional CNCs with random distributed nanoparticles, VA-CNTs offer three advantages: creating continuous paths through inter-VA-CNT channels for fast ion conduction, minimizing electrical conduction resistance due to the continuous CNTs, and by tailoring modulus anisotropically to enhance actuation strain. A large strain level of 8.2% is achieved in IPCNC actuators with VA-CNT/Nafion CNCs. Faster actuation combined with higher ionic conductivity has also been demonstrated.;Electrolytes providing for and transporting mobile ions are another component in IPCNC actuators. Traditional electrolytes, i.e. water and organic solvents have several issues including solvent evaporation and short lifetime. Ionic liquids with several unique features including nonvolatility, nonflammability, large electrochemical window, and high ionic conductivity, are introduced into IPCNCs, bring lots of opportunities for optimizing performance. The effect of ion size on actuator speed and efficiency has been investigated in IPCNCs with four imidazolium ionic liquids with different ion sizes. Besides single ions with different ion volume, the effect of ion clusters is identified in this dissertation by both experimental and theoretical approaches using ab initio method. The results could be utilized as guide in future IPCNC performance improvement.;Another class of EAP, the electrostrictive polymers (poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) P(VDF-TrFE-CFE)) are more mature for commercialized actuators and they are also studied in this dissertation. P(VDF-TrFE-CFE)) have large elastic energy density (1 J·cm-3 ) and are usually quite thin (thickness ∼1 microm) for operation voltage reduction. In this study several approaches for further improving their characteristics are discussed and demonstrated. The polymer blend approach is adopted to increase modulus by blending P(VDF-TrFE-CFE) with P(VDF-CTFE) (CTFE: chlorotrifluoroethylene). This approach results in alleviating of electrode clamping effect, i.e. strain reduction caused by electrodes. Electrical breakdown under high electrical field reduces device lifetime. Conductive polymers with a breakdown self-healing feature are employed as electrodes. The traditional deposition methods including in-situ polymerization and screen printing have several problems, such as taking a long time and damaging the thin polymer films. A mist spray method is developed for depositing conducting polymers with much increase deposition speed, improved coverage, less damage, and better thickness control (+/-0.1 microm). The low modulus of the conductive polymer further reduces the electrode clamping effect. An actuator with compact size (2mm diameter and 30mm length) and high performance (large displacement (1mm) and force output (1.5 N)) has been developed for refreshable full page Braille display and graphic display. These devices provide the capability for fulfilling so many dreams of the blind and visually-impaired. (Abstract shortened by UMI.)...