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Ionic polymer transducers (IPTs) are soft sensors and actuators which operate through a coupling of micro-scale chemical, electrical, and mechanical mechanisms. The use of ionic liquid as solvent for an IPT has been shown to dramatically increase transducer lifetime in free-air use, while also allowing for higher applied voltages without electrolysis. This work aims to further the understanding of the dominant mechanisms of IPT actuation and how these are affected when an ionic liquid is used as solvent. A micromechanical model of IPT actuation is developed following a previous approach given by Nemat-Nasser, and the dominant relationships in actuation are demonstrated through an analysis of electrostatic cluster interactions. The elastic modulus of Nafion as a function of ionic liquid uptake is measured using uniaxial tension tests and modeled in a micromechanical framework, showing an excellent fit to the data. Charge transport is modeled by considering both the cation and anion of the ionic liquid as mobile charge carriers, a phenomenon which is unique to ionic liquid IPTs as compared to their water-based counterparts. Numerical simulations are performed using the finite element method, and a modified theory of ion transport is discussed which can be extended to accurately describe electrochemical migration of ionic liquid ions at higher applied voltages. The results presented here demonstrate the dominant mechanisms of IPT actuation and identify those unique to ionic liquid IPTs, giving directions for future research and transducer development. / Master of Science

Opioid abuse and in particular fentanyl, a synthetic opioid, has been of concern in the last decade. Fentanyl is an illicit drug of concern to due to its prevalence and potency. Research to date has focused on supporting law enforcement by developing methods suitable for chemical profiling and identifying fentanyl from various matrices. However, methods geared towards analysis of fentanyl isomeric analogues are rare. Analysis of isomers is challenging due to similar mass spectral fragmentation patterns and exhibiting co-elution using common gas chromatographic columns. Developing methods to use in forensic labs utilizing already available equipment will advance current capabilities in the detection of fentanyl compounds. Thus, investigation into alternative stationary phases and development of special gas-liquid chromatographic (GLC) based methods for isomeric fentanyl analogues has been done. Several studies were done to investigate the use of ionic liquid chromatographic phases in analyzing fentanyl analogues. The first study focused on investigating the thermal stability of ionic liquids to identify those suitable to withstand the high oven temperatures that was needed to elute fentanyl analogues in gas chromatography. Total synchronous fluorescence spectroscopy and differential scanning calorimetry were demonstrated to be sensitive enough to detect the decomposition products of ionic liquids. In the second study, gas chromatographic analysis was done on fentanyl analogues using an ionic liquid stationary phase as well as two commonly used stationary phases for comparison purposes. The applicability of the developed methods was tested using standard fentanyl analogue samples as well as in-house synthesized samples on all three columns. In the third study, quantitative structure property relationship equations were developed to predict the retention time of fentanyl analogues on two of the gas chromatographic stationary phases used in the second study.

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Ionic polymer transducers (IPT) are a class of electroactive polymer devices that exhibit electromechanical coupling through charge transport in ionomeric membranes that contain a charge mobilizing diluent and are interfaced with conducting electrodes. Applications of these active materials have been broadly developed in the field of actuators and sensors. Advances in fundamental understanding of IPT performance mechanisms and tuning of the device components has primarily focused on transducers constructed with the commercial ionomer Nafion® due to its overall stability, high ionic conductivity, and availability. The much smaller number of studies conducted with non-perfluorosulfonated ionomers concentrated on changes in chemical composition to address processability, price, ionic conductivity, and hydrated modulus of the final IPT. Also, nearly all ionic polymer transducers operated with water as the diluent until the recent successful development of IPTs with ionic liquids. The objective of this research is to increase the understanding of electromechanical transduction in ionic polymer transducers through the synthesis and characterization of novel branched ionomers. Controlled branching is achieved in sulfonated polysulfones (sBPS) through employment of an oligomeric A₂ + B₃ step-growth polymerization. Structure – property relationships are established for a series of linear and branched sulfonated polysulfones to resolve the effects of polymer topology and charge content on ionomer properties such as hydrated modulus and ionic conductivity. Furthermore, the variation of these parameters is investigated in the presence of ionic liquids as a function of ionic liquid uptake using two methods for introduction of the diluent. One of those methods, based on casting of IPT components in the presence of the ionic liquid, was applied to the Direct Application Process to produce a controlled set of IPT electrodes and transducers to investigate percolation effects of RuO₂ on the device's electrical properties and actuation characteristics. Equivalent circuit modeling of the component and transducer electrical impedance accurately modeled variations in contributing processes and material interfaces to estimate the evolution of effective capacitance based on the electrode composition. Combination of optimized electrode composition, ionic liquid uptake, and the series of linear and branched sulfonated polysulfones allowed for fabrication of a tailored set of novel ionic polymer transducers. Effects of the fabrication process on the ionic conductivity of the membranes and transducers are evaluated using electrical impedance spectroscopy, which also allowed for equivalent circuit modeling to calculate effective capacitance for the series of IPTs that varied in composition, topology, and uptake for both types of fabrication processes. The transducers described in this dissertation are the first IPTs to be designed and actuated with novel ionomers, specifically linear and branched sulfonated polysulfones, in the presence of ionic liquids. Use of sulfonated polysulfones allowed for realization of transducers with high uptakes of the ionic liquid diluent that retained significant hydrated modulus on the order of 2 GPa. Characterization of electromechanical transduction for the series of sBPS – IPTs was demonstrated in cantilever bending through frequency response analysis and step responses in the time domain to low input voltages. Both the ion content and polymer topology of the sBPS ionomeric matrix demonstrated a significant effect on the final actuation performance in relation to variations in charge transport. Also, IPTs constructed with a co-diluent swelling method which emphasized the formation and stability of the ionomer's charge transport pathway demonstrated the greatest actuation responses, up to a peak-to-peak strain of ~0.45 % and strain rates on the order of 0.1 % / s while producing significant blocked force (180 N/Vm). Combination of these actuation performance metrics resulted in maximum energy densities of 1150 mJ/kg and 2.23 mJ/mm³ for the corresponding IPT. / Ph. D.

Thesis (MSc)--Stellenbosch University, 2004 / ENGLISH ABSTRACT: In an ongoing study an empirical force field that can correctly model N,N'- dialkylimidazolium halide ionic liquids, the Imidazolium Ionic Liquid Force Field - IILFF, was developed based on experimental data obtained from the Cambridge Structural Database (CSD) and data calculated using Gaussian98. Different conformations of the isolated cations were optimised at the Hartree-Fock level using the 6-31G(d) basis set. Structural, vibrational and partial atomic charge data of the lowest energy conformation of each cation were taken as observables during optimisation of the force field parameters. Initial parameters of the IILFF were taken from existing force fields and were optimised using the above mentioned data. The IILFF was used to minimise isolated cations as well as crystals. These results were successfully tested against isolated cations minimised using Gaussian98 and the experimental crystals. Finally, the melting process of the 1,3-dimethylimidazolium chloride crystal was studied using an NPT ensemble starting from an ordered crystal cell and increasing the simulation temperature beyond the experimental melting temperature. The IILFF was then used to calculate the potential energy of the system. / AFRIKAANSE OPSOMMING: In 'n voortgaande studie om 'n empiriese kragveld te bou wat N,N' -dialkielimidasoliumhalied ioniese vloeistowwe korrek kan modelleer is die Imidasolium Ioniese Vloeistof Kragveld (nVK) ontwikkel. Die kragveld is ontwikkel gebasseer op eksperimentele data verkry uit die Cambridge Strukturele Databasis (CSD) asook uit data vanaf Gaussian98 berekeninge. Verskillende konformasies van die geïsoleerde katione is geoptimiseer deur middel van Hartree Fock 6-31G(d) berekeninge. Strukturele data, asook vibrasies en gedeeltelike atoom ladings van die laagste energie konformasie van elke katioon is gebruik as waarneembare veranderlikes vir die bepaling van die optimale kragveld parameters. Beginwaardes vir die nVK is geneem uit bestaande kragvelde en geoptimiseer met behulp van bogenoemde data. Die IIVK is gebruik om geïsoleerde katione asook kristalle te minimiseer. Die resultate is suksesvol getoets teen geïsoleerde katione wat met behulp van Gaussian98 geminimiseer is en eksperimenteel bepaalde kristalle. Laastens is die smeltproses van die 1,3-dimetielimidasolium chloried kristal bestudeer met behulp van 'n NPT ensemble. Daar is begin by 'n geordende kristal en die simulasie temperatuur is verhoog tot meer as die eksperimentele smeltpunt. Die IIVK is dan gebruik om die potensiële energie van die sisteem te bepaal.

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