Aqueous Binary Mixtures A Study Using NMR Measurements and ab initio Molecular Dynamics Simulations

Abstract

Binary mixtures having a combination of hydrophobic and hydrophilic groups, such as waterdimethyl sulfoxide (DMSO), water-methanol, water-ethanol, water-tertiary butyl alcohol (TBA), water dioxane, and water-glycerol, have been widely studied. These mixtures often show non-ideal mixing behaviour with properties such as electrical conductivity, permittivity, speci fic volume, enthalpy of mixing and light-scattering behaviour exhibiting non-monotonic behaviour as a function of the composition of the mixture. The waterethanol system that is miscible over the entire composition range is perhaps one of the most elementary but nontrivial model system that exhibits non-ideal behaviour. The mixtures exhibit negative excess entropy and a strong increase in heat capacity as compared to an ideal solution, with properties such as, molar volume, excess entropy, compressibility, viscosity, diffusion coeffcient, and sound attenuation coeffcient exhibiting composition dependent anomalies. The occurrence of different solvation regimes in water-alcohol binary mixtures has been widely reported, although the values of the transition points, the mole fraction of alcohol in the mixture, show minor differences depending on the experimental technique. It is generally accepted that the anomalous properties of aqueous binary mixtures is a consequence of the perturbation of the local and global hydrogen bond network due to the presence of the second component. Despite a large number of investigations encompassing both theories and experiments, a molecular understanding of the anomalous properties of the water-ethanol system has remained elusive. The focus of this thesis is on the role of hydrogen bonding and the modi fication of the hydrogen bonding network due to the presence of the second component in water-ethanol and water-ethylene glycol systems using solution Nuclear Magnetic Resonance (NMR) spectroscopy aided by ab initio Molecular Dynamics (AIMD) simulations for interpreting the experimental observations...