Local Dynamics of Molecules in a Molecular Ionic Composite Electrolyte

Abstract

At the molecular level, thermal energy causes molecules to move randomly, including rotational motion. These rotational dynamics are measured by using the rotational correlation time (τ_c). Rotational correlation time describes the average timescale over which a molecule changes its orientation by about one radian through random thermal motion. Nuclear Magnetic Resonance (NMR) is sensitive to the rotational motion of molecules on the picosecond to nanosecond time scale, depending on the magnet's external magnetic field strength. The average root-mean square displacement of molecules during this rotational motion is on the Å scale. Rotational correlation time provides insight into the local environment of molecules, where longer correlation times suggest stronger local associations or restricted motion. These molecular-level insights can guide the design of next-generation ionic liquids (ILs) for electrochemical devices such as batteries. This thesis provides a framework for directly measuring τ_c of molecules such as ionic liquids on the picosecond timescale using NMR relaxation techniques. This thesis provides a framework for directly measuring the τ_c of molecules such as ionic liquids on the picosecond timescale using NMR relaxation techniques. It investigates changes in the rotational correlation time (τ_c) of cations and anions in the presence of fixed anionic groups on the rigid-rod polymer, compared to the ionic liquid state. It is hypothesized that the fixed anion on the rigid-rod polymer will alter the local dynamics of both cations and anions compared to their behavior in the ionic liquid state. In addition, this study helps evaluate how strongly the cations of the ionic liquid are associated with the fixed anionic groups on the rigid-rod polymer.