| dc.description.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.
In summary, this thesis has attempted to show how 1H NMR measurements in combination
with ab initio MD simulations can be used to probe H-bonding and the nature of
association in aqueous-binary mixtures of ethanol and ethylene glycol. The strategy was to
first establish a geometrical de nition of H-bonds in pure ethanol and ethylene glycol before
attempting the same for aqueous-binary mixtures. It is shown here that the secondary
isotope effect can be used to distinguish intra and intermolecular interactions in the 1H
NMR of mixtures of ethanol and ethylene glycol along with deuterted counter parts. It is
shown how 1D transient NOE measurements of these mixtures, in conjuction with AIMD
simulations can establish the geometry of H-bonds in pure ethanol and ethylene glycol. A
simple procedure to determine the geometry of H-bonds between different donor-acceptor
pairs ethanol-ethanol, water-ethanol and water-water in water-ethanol mixture from fragment
obtained from AIMD is outlined. Having established the geometry of H-bonds it is
possible to determine the thermodynamics of hydrogen bond formation in water-ethanol
system at different compositions. The nature of association in the aqueous-binary mixtures
could be established by 1H NMR measurements. The fact that there are water-rich and
ethanol-rich clusters in dynamic equilibrium could be established from these measurements.
The results presented in this thesis could pave the way for a better understanding, at the
molecular level, intriguing properties of binary mixtures using a combination of NMR
measurements and molecular dynamics simulations. | en_US |
