Molecular diffusion as measured by pulsed field gradient nuclear magnetic resonance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University

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Massey University
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The work presented in this thesis may be conveniently divided into three sections. Firstly the development of a Carr-Purcell-Meiboom-Gill pulse sequence for use in the pulsed field gradient experiment in order to examine diffusion over long diffusion times is described. Secondly diffusion coefficients of both components of binary mixtures of methanol and benzene have been measured using pulsed field gradient fourier transform NMR. Results showed self-association to be dominant over AB association and a brief qualitative explanation of the reasons for this is given. In the third section, which is the major part of this thesis, diffusion coefficients of water in the caesium perfluoro-octanoate, water system have been determined at various weight fractions and temperatures by pulsed field gradient NMR. The liquid crystalline phases occuring within the system are the isotropic micellar solution, the nematic amphiphilic mesophase and the smetic lamellar mesophase. Water was found to pass through the system in an unrestricted and virtually unhindered manner. These results were discussed in terms of the known structures of the phases and with respect to possible permeation mechanisms. No definite conclusion as to the permeation mechanism is possible. The limitations in the use of surfactants as membrane models is discussed.
Molecular dynamics, Nuclear magnetic resonance, Diffusion