Bawazeer, Tahani Mohammad (2012) Developments of new techniques for studies of coupled diffusional and interfacial physicochemical processes. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Confocal microscopy, Ultramicroelectrodes, Scanning electrochemical microscopy, Electrochemistry
Official Date:	December 2012
Dates:	Date Event December 2012 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Unwin, Patrick R.
Sponsors:	Saudi Arabia. Wizārat al-Taʻlīm al-ʻĀlī [Saudi Arabia. Ministry of Higher Education]; Jāmiʻat Umm al-Qurá [Umm Al-Qura University]
Extent:	xix, 158 leaves : illustrations.
Language:	eng

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