Date of Award

2009

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Chemistry and Biochemistry

Keywords

Pure sciences, Aminophenol, Chemical oscillators

Supervisor

Jichang Wang

Rights

info:eu-repo/semantics/openAccess

Abstract

Designing new chemical and/or electrochemical oscillatory systems is an important area in nonlinear chemical dynamics. We successfully designed two new chemical oscillators, the pyrocatechol-bromate-sulfuric acid and aminophenol-bromate-sulfuric acid systems. Both chemical systems exhibit a very rich oscillatory behavior and we obtained their phase diagrams in uncatalyzed and ferroin-catalyzed systems. Phase diagrams in the bromate - pyrocatechol - sulfuric acid concentration space illustrate that the observed chemical oscillations strongly depend on the ratio of [bromate]/[pyrocatechol] rather than their actual concentrations. Also, in both uncatalyzed and catalyzed systems kinetics and mechanisms have been investigated. In mechanistic studies, we have tried to determine intermediate species with various analytical techniques such as: FTIR., 1H NMR, 13C NMR, Mass spectroscopy, TLC, Elemental Analysis, etc.

The aminophenol system is found to be a photo-mediated oscillatory system which does not exhibit spontaneous oscillations in the absence of light. Investigation of the role of illumination, in particular the wavelength of light responsible for the oscillatory behaviour, in the aminophenol-acidic bromate system has been carried out. Study shows that the long induction time in this photochemical oscillator has an exponential dependence on the light intensity. On the other hand, the pyrocatechol system is a photosensitive oscillatory system which light is capable of quenching and inducing oscillation in the system.

Furthermore, chemical wave activities in the ferroin-catalyzed pyrocatechol system have been investigated, in 2-dimensional (2-D) beads and homogeneous systems, and in a 1-dimensional (1-D) medium. In the 1-D pyrocatechol system, we observed various types of pulse instabilities such as: breathing, propagation failure, merging pulses, and packing phenomena. In the homogeneous 2-D medium, the pyrocatechol system exhibited two stages of wave activity. Spontaneous transitions to complex spatiotemporal patterns, as a result of anomalous dispersions, have also been observed. In the beads pyrocatechol system, variation of wave propagation speeds and spiral tip trajectories versus four different factors including concentrations of bromate, acid, and ferroin concentration and beads mass have been characterized.

Wave studies in the 1-D aminophenol system showed different types of pulse instabilities as well, where global breathing phenomena lasted for more than 48 hours in most cases. In 2-D reaction diffusion media in bead, the ferroin-catalyzed aminophenol system is capable of supporting slow waves even in the absence of light.

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