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Title: Developments of new techniques for studies of coupled diffusional and interfacial physicochemical processes
Author: Bawazeer, Tahani Mohammad
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2012
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This study is concerned with the development and application of electrochemical techniques combined with confocal laser scanning microscopy (CLSM) as a probe of the kinetics of electrochemical and surface reactions at different interfaces. A CLSM set up has been designed which combines electrochemical and microscopic techniques to extend the applications of CLSM in a new research fields. This methodology has been applied to various electrochemical systems in this thesis. The electrochemical activity of ultramicroelectrodes (UMEs) has been quantified using CLSM. A special optically transparent electrode, comprising a thin film of carbon nanotube network has been developed for these studies. The methodology comprises of tracking the dynamic, reversible concentration profiles of electroactive and photoactive tris(2,2'- bipyridine)ruthenium(II) species in aqueous solutions during cyclic voltammetry experiments. A decrease of the solution intensity is recorded at and around the UME surface during the oxidation of luminescent Ru(bpy)3 2+ to non-luminescent Ru(bpy)3 3+, followed by an increase of the intensity signal in the reverse scan direction as the oxidized Ru(bpy)3 3+ is consumed at the electrode surface. A three dimensional map of the concentration gradients of Ru(bpy)3 2+ is constructed by collecting sections of the object across the normal to the electrode plane at the steady state current regime. The first use of CLSM coupled with scanning electrochemical microscopy (SECM) has been introduced as a means of time dependent visualisation and measurement of proton dispersion at dental enamel surfaces and the effectiveness of inhibitors on substrates. This new technique provides an analytical method with high spatial and temporal resolution permitting sub-second analysis of treatment effects on enamel substrates. In this case the UME tip of SECM is used to generate protons galvanostatically in a controlled manner and the resulting proton fields were quantified by CLSM using a pH sensitive fluorophore. Given the advantage of SECM to deliver high controllable, and local acid challenges in a defined way, and the high temporal and spatial resolution in the millisecond and micrometer range, respectively, in CLSM allows the surface kinetics of dissolution and the effect of barriers on the enamel surfaces to be evaluated. Finite element model has been used to describe the dissolution process, which allows the kinetics to be evaluated quantitatively, simply by measuring the size of pH profiles over time. Fluoride and zinc were used as treatments for enamel surfaces to investigate the effect of inhibitors on proton distribution, since they are generally considered to impede the dissolution process. Proton lateral diffusion at modified surfaces was also investigated using CLSM and SECM to validate the use of these techniques. A disc UME was brought close to the membrane and the oxidation of water was induced. Proton lateral diffusion was observed as a change in pH along the membrane. Different electrostatic interactions were investigated by functionalising the surface with different phospholipid head group and polypeptide multilayer films, since they are thought to have an effect on facilitate or retreat the process. Anionic lipids head groups share protons as acid-anion dimmers and thus trap and conduct protons along the head group domain of bilayers that contain such anionic lipids. The results also indicate the rate and mobility of proton diffusion along membrane are largely determined by the local structure of the bilayer interface.
Supervisor: Not available Sponsor: Wizārat al-Taʻlīm al-ʻĀlī (Ministry of Higher Education, Saudi Arabia) ; Jāmiʻat Umm al-Qurá (Umm Al-Qura University)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry