Nonlinear dynamics of acid- and base-regulated chemical systems

Abstract

Interest in the interdisciplinary field of nonlinear dynamics has increased significantly over the past three decades. Nonlinear dynamics is the study of the temporal and spatio-temporal evolution of dynamical systems whose behaviour depends on the values of the key variables in a nonlinear manner. Nonlinear chemical reactions, chemical oscillations and their spatial behaviour play an important part in the field of nonlinear dynamics. This thesis is concerned primarily with those chemical systems which feature the proton, or its counterpart the hydroxide ion, as a main kinetic driving species. A review of the area is presented to provide a background for the developments discussed in this thesis. Experimental and numerical investigation of the methylene glycol-sulfite reaction leads to the development of a complete kinetic model for this system. This new mechanism provides the basis of a reduced model for the design of novel pH oscillators. This reduced model, discussed in chapter 4, is used to design the first organic substrate based, non-redox, pH oscillating reaction, the methylene glycolsulfite-gluconolactone system. In an open reactor this reaction displays large amplitude oscillations in pH which are well modelled with a proposed mechanism. In chapter 5 experimental results of an acid autocatalytic reaction performed in nano-meter size water droplets are presented. The effects of confinement on the kinetics is established and shown to be affected by changes in droplet size and dispersion of droplets. The effect of the microheterogeneties of the microenvironment on reaction-diffusion fronts in this system is also investigated. The results show the propagation of acid fronts with interesting structural instabilities