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Effects of Electrode Surface Morphology on the Transduction of Ionic Polymer-Metal Composites
Chemical and Materials Engineering
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Ionic polymer-metal composites (IPMCs) are innovative smart materials that exhibit electromechanical and mechanoelectrical transduction (conversion of electrical input into mechanical deformation and vice versa). Due to low driving voltage (< 5 V) and ability to operate in aqueous environment, IPMCs are attractive for developing soft actuators and sensors for underwater robots and medical devices. This dissertation focuses on investigating the effects of electrode surface morphology in the transduction of Pt and Pd-Pt electrodes-based IPMCs, with the aim to improve the electrode surface design and thereby enhance the transduction performance of the material. Firstly, the synthesis techniques are developed to control and manipulate the surface structure of the mentioned electrodes through the electroless plating process. Using these techniques, IPMCs with different electrode surface structures are fabricated. The changes in the electrode surface morphology and the resulting effects on the material's electromechanical, mechanoelectrical, electrochemical and mechanical properties area examined and analyzed. This study shows that increasing the impregnation-reduction cycles under appropriate conditions leads to the formation and growth of platinum nanoparticles with sharp tips and edges - called Pt nanothorn assemblies - at the polymer-electrode interface. IPMCs designed with such nanostructured Pt electrodes are first to be reported. The experiments demonstrate that the formation and growth of Pt nanothorn assemblies at the electrode interface increases considerably the total transported charge during the transduction, thereby increasing significantly the displacement and blocking force output of IPMC. The improvement of the mentioned electromechanical properties was 3-5 times, depending on the input voltage and frequency used. Also, the peak mechanoelectrically induced voltage increased somewhat, although the overall effect of the surface structure was relatively low compared to the electromechanical transduction.The Pd-Pt electrodes-based composite systems are introduced due to their unique highly capacitive palladium inner surface layer. It is shown that by controlling the impregnation time in Pd complex solution during the electroless plating process leads to changes in the amount and distribution of porous palladium at the inner surface of the polymer membrane, which greatly affects the IPMC transduction. The results show that increasing the dispersion of Pd particulates in the polymer matrix increases noticeably the total transported charge and the resulting electromechanical output of IPMC. A three-fold increase in both displacement and peak blocking force was achieved by varying the impregnation time accordingly. Also, noticeable effect on the induced voltage amplitude was observed.