Nanostructured electroactive polymer actuator materials.

摘要

This dissertation investigates nanostructured materials, including the nanorods of Field Activated Electro Active Polymer (FEAP) and Ionic Electro Active Polymer (IEAP) systems. As one of the most important FEAPs, the large electromechanical responses in the ferroelectric relaxor poly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) P(VDF-TrFE-CFE) terpolymers make them attractive to nanoelectromechanical systems (NEMS), as well as nanoactuator and nanosensor applications. This dissertation develops the fabrication process for the nanorod array of P(VDF-TrFE-CFE) relaxor ferroelectric terpolymer using an anodic aluminum oxide (AAO) template. Nanorod arrays in the rod diameter have been fabricated down to 25 nm.;In the relaxor ferroelectric terpolymers, the bulky CFE monomers act as the random defects that break the long range polar-ordering in the ferroelectric P(VDF-TrFE), and the freezing of the random dipoles leads to the relaxor behavior. Making use of the nanorod arrays, the evolution of the relaxor ferroelectric behavior of the P(VDF-TrFE-CFE) terpolymers was investigated for nanorods with diameters reduced from 200 nm to 25 nm. It was observed that all the nanorods exhibited relaxor ferroelectric behavior, as characterized by the dielectric peak shifting toward high temperatures with frequency. The frequency-permittivity peak temperature characteristics fit well with the Vogel-Fulcher-Tammann (VFT) relation. Moreover, the freezing temperature in the VFT relation decreases with the reduction of the nanorod diameter, indicating that the reduction of the nanorod's diameter influences the relaxor ferroelectric behavior of the terpolymer. The existence of ferroelectric relaxor properties in terpolymer nanorods as small as 25 nm suggests the possibility of terpolymers for NEMS and nanoactuator applications. It also provides an interesting ferroelectric material system with which to study the finite size effect in ferroelectric relaxor.;In the IEAPs, the ions transport through the ionic systems under an applied field and the subsequent accumulation and depletion of excess ions at the electrodes determine the response behavior of the electroactive devices, such as IEAP actuators and supercapacitors. Moreover, recent experimental results reveal the potential of ionic liquids (ILs) in enhancing the IEAP device performance. For instance, the vapor pressure of ILs is negligibly low and as a result they will not evaporate out of the IEAP devices when operated in ambient conditions. Their wide electro-chemical window (∼4 V) allows the IEAP to utilize higher applied voltages than the dilute water solution electrolyte. ILs also offer the possibility of achieving high mobile ion concentration and high ion mobility. This dissertation investigates the charge dynamics of ILs in two kinds of nanostructured IEAPs, which possess distinctively different polymer nanomorphologies, and it is of great interest to know how these morphologies affect the charge dynamics of ILs.;A time domain electrical characterization method was developed and employed to systematically study the charge dynamics of ILs in these IEAPs. Compared with the frequency domain method, this method offers the possibility of probing the charge dynamics over a broad voltage range. In the Aquivion membrane swelled with EMI-Tf, the ionic conductivity and mobility show strong uptake dependent behaviors and undergo abrupt enhancement transitions close to the critical uptake, which suggests that the minimum uptake for the IEAP application is above its critical uptake. It was found that the ionic conduction of ILs is coupled with the segmental motion of the ionic phase of the Aquivion membrane implying that the enhancement of the ionic conduction is mainly due to the reduction of the glass transition temperature of the ionomer matrix with an increased uptake of EMI-Tf. The activation energies for ions to dissociate do not show substantial uptake dependence. With the same uptake of EMI-Tf, both Aquivion and Nafion show almost the same charge dynamics, while the short side chain Aquivion shows a better electromechanical coupling per charge than that of the longer side chain Nafion. (Abstract shortened by UMI.).