Thesis defense of Jennifer Bolle

Understanding the microstructure of selfassociated fluids promoted by hydrogen bonding and constrained by steric hindrance is of great importance to chemistry, physics, biology, and many aspects of daily life. In this work, a combination of X-ray diffraction experiments, dielectric spectroscopy, and molecular dynamics simulations is used to study thermodynamic changes in the microstructure of various monohydroxy alcohols. Here, the microstructure is constructed of linear, cyclic, and more complex structures separated by outwardly directed alkyl chains. This clustering is analyzed by interpreting the change in intermolecular distances calculated from scattering intensities. The charge order that results from OH aggregation via hydrogen bonds can be related to the relaxation strength of the Debye process, in the dielectric response of the system. The complementary measurement methods thus provide a valuable insight into the effects of molecular architecture and thermodynamic conditions on this structure formation. This reveals a change in microstructure with a decrease in temperature, increase in pressure, and enhancement of steric hindrance. The results indicate that longer, linear aggregates form preferentially at low temperatures. This formation is promoted by ring opening effects and play a crucial role especially for molecules with larger steric hindrance. Here, due to the shielding of the OH group, cyclic clusters with 4-6 molecules are formed more frequently. These ring-opening effects can not only be induced thermally, but also occur when the pressure is increased. Here, ring structures as well as linear arrangements are clearly disturbed and the number of molecules in a cluster strongly decreases. These results provide an insight into the structure formation of monohydroxy alcohols as a function of different thermodynamic conditions and the variability of their molecular architecture.

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