Image Charge Effects Near Solid Surfaces

Citation

Ye, Benjamin Bobin (2025) Image Charge Effects Near Solid Surfaces. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fjpq-wn07. https://resolver.caltech.edu/CaltechTHESIS:07262024-075858049

Abstract

Ion–surface interactions underpin fundamental biological and technological processes and hold the key to advancing the performance of modern electrochemical devices, such as electric double-layer capacitors (EDLCs). As such, a comprehensive understanding of the mechanistic details governing these interactions and their effects on the electrical double layer structure and charge transport is crucial. However, accurately modeling ion–surface interactions in theory and simulations remains challenging due to the complexities and computational cost associated with properly treating dielectric discontinuities at ion–surface interfaces. This thesis leverages the efficient method of image charges in coarse-grained molecular dynamics simulations to capture the correct behavior at the ion–surface interface and unravel anomalous phenomena in various charged soft matter systems with conductive metal surfaces. Specifically, we construct a molecular model to demonstrate a spontaneous symmetry breaking transition in room-temperature ionic liquid EDLCs that provides a molecular mechanism for a hysteresis in the capacitance behavior observed experimentally. We also introduce a physically motivated soft-core model, the Gaussian core model with smeared electrostatics (GCMe), which addresses the limitations of traditional hard-core force fields in representing bulky organic ions and their spread charges, while also being orders of magnitude faster. Using GCMe, we then characterize the effects of the polyelectrolyte chain length, electrolyte polarizability, and electrode material on the energy storage of polymerized ionic liquid EDLCs, and the ion adsorption behavior and charging/discharging dynamics in polyelectrolyte EDLCs. Finally, we present MDCraft, an open-source Python assistant designed to streamline computational research workflows by providing tools for simulation setup, data analysis, and visualization. This comprehensive study not only enhances the understanding of ion-surface interactions but also offers practical insights and tools for advancing the design and optimization of systems involving charged species near surfaces, such as next-generation electrochemical energy storage devices.

Thesis Files