Halliday, Nicola Ann (2011)
Ph.D. thesis, University of Birmingham.
The work presented in this thesis has investigated the development of magnetic resonance (MR) techniques to probe the pH in aqueous solutions and reverse micelles formed in CTAB, Triton-X and AOT microemulsions. These techniques have enabled visualisation of propagating acidity fronts in the bromate-sulfite reaction using magnetic resonance imaging. Contrast agents that are sensitive to pH were investigated in aqueous and microemulsion media. Successful magnetic resonance imaging of the aqueous system was achieved using the pH-dependent chelation of the paramagnetic species Cu(II), with the chelating ligand triethylenetetramine. However, it was found that MR contrast agents were not required for probing the pH in reverse micelles of the CTAB and Triton-X microemulsions. Magnetic resonance imaging of the bromate- sulfite reaction in a CTAB microemulsion system was achieved without the need for additional probe molecules or contrast agents and was found possible following investigations of pH in reverse micelles of the microemulsion using MR relaxation times. T_2 relaxation times of water in the CTAB and Triton-X microemulsions were found to change with pH, however, T_1 relaxation times remained unaffected. This behaviour was attributed to acid-catalysed exchange between protons of water and hydroxyl protons of the cosurfactant alcohol in these systems. These findings present the first direct monitoring of pH in reverse micelles of microemulsion systems without the need for probe molecules
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