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Gravimetric and Viscoelastic Investigation of Electroactive Films

By Mohamoud Abdirahman Mohamoud

Abstract

Gravimetric and viscoelastic studies of thin electroactive polymer films and self-assembled monolayers were carried out using (non)-electrochemical techniques; notably cyclic voltammetry, EQCM and crystal impedance. Mobile species dynamics accompanying film redox switching due to thermodynamic and electroneutrality constraints were theoretically modeled and experimentally determined. In a novel approach, 3D visual models of solvent and ion transfers under mixed control of thermodynamic and kinetic conditions were described. For the identification of change in behaviour at partial conversion during film redox transformations, flux ratio representations were introduced. Applications of the theoretical models to polyaniline data in EQCM experiments revealed that film solvent population was in equilibrium on the experimental timescale but showed thermodynamic non-ideality. Mass and charge responses of polyaniline gravimetric data were described by a mechanism in which electroneutrality maintenance was satisfied by a mixed transfer of proton and anion.\ud Adsorption/desorption mechanisms of dendrimer on flavin-functionalised surfaces were gravimetrically determined. The energetics and isotherm models of the adsorption/desorption process were investigated. Frumkin model was found to best fit to the experimental data and site-site interaction parameter was extracted.\ud Viscoelastic investigations of polyaniline in electrochemical systems were studied. The effects of different anions on film rheological properties during deposition and redox cycling were explored. Shear moduli data were extracted as functions of potential, temperature and timescale using TSM resonator. In an unprecedented manner, macroscopic viscoelastic properties of polyaniline films were described at a molecular level using WLF, Rouse-Zimm, and Activation models. The “time-temperature superposition” principle was applied and the master relaxation curve was constructed. In correlation between solvent content and film structural dynamics, the energetics of solvation were calculated. From thermal dependent viscoelastic responses of the film, glass transition temperature, thermal expansion coefficient and fractional free volume of polyaniline were determined

Publisher: University of Leicester
Year: 2007
OAI identifier: oai:lra.le.ac.uk:2381/9941

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