Resonant X-ray scattering studies of concentrated aqueous solutions

The microscopic structure of concentrated aqueous electrolyte solutions has been studied by resonant X-ray diffraction (RXD). This technique provides a method for the measurement of the structure around a specific atom or ion in solution. In that sense, RXD is the X-ray equivalent of neutron diffraction with isotopic substitution (NDIS). The use of RXD as an alternative to NDIS has been considered of interest for some time; it is potentially one of the best methods for overcoming the most important limitation of the neutron diffraction technique, i.e. the lack of suitable isotopes for every atomic species. Third generation synchrotron sources offer an unprecedented opportunity for the further development of RXD to study the microscopic structure of liquids and amorphous materials. One of the main aims of this thesis was to check whether it could be possible to obtain results of comparable accuracy to those of NDIS. In this work, the hydration structures of Br"-, Rb"+, Sr"2"+ and Y"3"+ in concentrated aqueous solutions have been studied by RXD. A detailed account of how the experiments were carried out and the data analysis procedure is given. The results are compared with those obtained for the same ion by other techniques and to those obtained for similar systems by NDIS. The reliability of these results and the observed trends in the measured structure when compared to other ions in the same series are discussed. A comparative study of the structure of the three cations is also presented in this thesis. This work illustrates one of the main advantages of RXD: the possibility of carrying out systematic structural studies on all elements with atomic number greater than 28 (Ni). Finally, a critical discussion on the actual stage of development of RXD is presented. The results shown offer evidence of the future prospects of the technique and justify further efforts to develop it to the level of reliability and ease of use that NDIS has reached after more than three decades of development. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN051178 / BLDSC - British Library Document Supply CentreGBUnited Kingdo