STRUCTURE-PROPERTY RELATIONSHIPS IN TWO-COMPONENT LIQUIDS

Abstract

This thesis tackles several two-component liquids where we currently have a poor understanding of their fundamental structures and influence on properties. A novel approach was taken to investigate hydrophobic interactions.1 Rather than studying the aqueous liquid, for which only very low hydrophobe concentrations are possible, the metastable glassy state formed by thermally annealing a H2O/C60 fullerene vapour deposit was examined. These ‘trapped solutions’ of fullerene in an amorphous solid water (ASW) matrix were prepared in newly built apparatus (Chapter 3) using deposition rates of about 5 H2O monolayers per second to give a total mass > 1 g without crystalline ice contamination. H2O desorption rate analysis indicated that the limits of ASW growth are associated with the influence of deposition rate on porosity and consequent decreases in deposit to cooling plate heat transfer with increasing deposit thickness. Characterisations by FT-IR, Raman, optical absorbance and photoluminescence spectroscopies, as well as by X-ray and neutron diffraction showed unexpected continual structural relaxation until their crystallisation to ice I at 150–160 K (Chapter 4).2 Contrary to Frank and Evans’s description of ‘iceberg’ hydration structures,3 for C60 in ASW there is a weakening of the average hydrogen bonding interaction and increases in dynamics of the first hydration layer. The present work tentatively supports theories of hydrophobic hydration forces involving a disconnection of water in the hydration shell from the extended hydrogen bonding network (Chapter 5).4-5

The intermolecular interactions in the chloroform–acetone (negative) and benzene–methanol (positive) azeotropes were investigated by Raman spectroscopy and neutron diffraction. Structural models of pure liquid chloroform and the chloroform-acetone azeotrope were prepared by Empirical Potential Structural Refinement6 of experimental data and described using radial distribution functions, spatial density functions, orientation correlation functions and Kirkwood correlation factors. These analyses revealed that ‘super dipole’ Cl3H - Cl3H - Cl3H self-associations in pure liquid chloroform (29 % molecules) may contribute to its good solvent quality and anaesthetic properties (Chapter 6),7 and that C2H6O - HCCl3 hydrogen bonding interactions are present in the chloroform-acetone azeotrope (Chapter 7). Through comparisons of radial distribution functions between ‘like’ and ‘unlike’ species in the azeotropes it is revealed that the azeotropic vapour pressure condition is not only characterised by the non-ideality of intermolecular interaction but also by significant deviations in mixing character from that of a regular mixture; the benzene-methanol azeotrope exhibit microscopic statistical demixing and the chloroform-acetone azeotrope exhibits transient complexation.