Doctoral Dissertations
Date of Award
8-2022
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Physics
Major Professor
Dr. Takeshi Egami
Committee Members
Dr. Michael Fitzsimmons, Dr. Steven Johnston, Dr. Cristian Batista, Dr. Thomas Papenbrock
Abstract
Liquid state physics remains relatively unexplored compared to solid-state physics, which achieved massive progress over the last century. The theoretical and experimental methodologies used in solid-state physics are not suitable to study the liquid state due to the latter's strong time dependence and the lack of periodicity in structure. The approaches based on phonon dynamics break down when phonons are over-damped and localized in liquids. The microscopic nature of atomic dynamics and many-body interactions leading to liquid state properties such as viscosity and dielectric loss in liquids remain unclear. Inelastic neutron scattering measurements were done to study the microscopic origins of the above phenomena on two liquid state systems, water and gallium, with the atomic dynamics explored in real-space and time utilizing the Van Hove function, G(r,t). Molecular Dynamics (MD) simulations were implemented to explain the experimental observations. The Local Configurational Excitation (LCE) is the fundamental excitation that changes the topology of local connectivity in liquids. The life-time of LCE () is defined as the time it takes for an atom to lose or gain a neighbor. It was proposed through MD simulations, and later verified through neutron scattering measurements that the LCE’s are the microscopic origin of viscosity in metallic liquids at high temperatures. Generalizing this study to different types of liquids is essential to obtain a universal dynamical behavior of liquids. Towards that goal, we studied the correlated dynamics of a partly covalent liquid, gallium. We show that it is possible to achieve a universal behavior for simple metallic liquids and partially covalent liquid metals. The high dielectric loss in water is one of the anomalous properties of water. The microscopic molecular mechanism leading to this property remains unclear despite decades of research. By determining the Van Hove function of water from inelastic neutron scattering measurements, we show that the origin of the high dielectric loss is a collective reorientation of water molecules and cooperative proton tunneling involving several water molecules. The results contradict the widely held beliefs that the dielectric relaxation mechanism in water involves the rotation of a single molecule and is purely diffusive in origin.
Recommended Citation
Sarathchandran, Yadu Krishnan, "Understanding Liquid Dynamics using the Van Hove function from Inelastic Neutron Scattering Measurements. " PhD diss., University of Tennessee, 2022.
https://trace.tennessee.edu/utk_graddiss/7398