Thema der Dissertation:
Structure and Dynamics of Molecular Liquids: From Bulk Behavior to Nanoconfinement via Computational Spectroscopy
Structure and Dynamics of Molecular Liquids: From Bulk Behavior to Nanoconfinement via Computational Spectroscopy
Abstract: Despite their seemingly simple chemical composition, many molecular liquids exhibit complex behaviors that arises from their intermolecular structure: while they seem disordered on the macroscale, they feature locally ordered environments on the microscopic scale. At interfaces with other substances, the liquid's organization is altered due to chemical interactions with the opposing substance and the interfacial geometry. The local interfacial structure of liquids determines key physicochemical properties, such as wettability and surface reactivity. When a liquid is further constrained by confining it to a nanoscopic space, they undergo additional structural perturbations, leading to the emergence of unique and exotic behaviors. Characterizing the microscopic structure of molecular liquids and relating it to their macroscopic properties stands as a central challenge in chemical physics. Among the various experimental techniques employed to study the microscopic structure of liquids, spectroscopic methods sensitive to intra- and intermolecular vibrations of molecules have proven especially successful. However, interpreting experimental spectroscopic data in terms of molecular motion and structure is still not fully understood, as the high degree of collectivity in the dynamics of molecular liquids complicates the identification of spectral features with simple molecular mechanisms.
The present thesis employs molecular modeling techniques that resolve the local liquid structure and dynamics, while establishing relations between modeling results and experimental observables through concepts from statistical mechanics. We focus on liquid water, whose hydrogen bond network is paradigmatic for the complex intermolecular structure of molecular liquids, and perfluorinated hydrocarbons, a synthetic organic liquid of industrial significance, and analyze how external constraints, in the form of single interfaces and nanoconfinement, alter their molecular structure. In the bulk phase, we illustrate how signatures of the highly collective vibrational behavior in the linear absorption spectrum of perfluorinated hydrocarbons can be interpreted with the help of different molecular modeling methods and establish a method to uncover the influence of varying conformational dynamics on vibrational line shapes. We then discuss the structure of water at the interface to fluorinated surfaces. There, anisotropic orientation of water molecules gives rise to local electric fields and specific vibrational signatures, which we contextualize with the available experimental data. Finally, we analyze the influence of geometric confinement on the hydrogen bond network of liquid water. We propose a decomposition of linear absorption spectra to distinguish between bulk, interfacial, and confinement effects, allowing us to identify signatures of long-range collectivity in the vibrations of nanoconfined water.
Zeit & Ort
01.12.2025 | 14:00
Hörsaal B (0.1.01)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)