UC Berkeley

At the interface, molecules experience local environments defined by anisotropic forces, disrupted solvation structures, and steep spatial gradients. These conditions can influence reaction pathways in ways that are not captured by bulk-phase experiments or models. Interfaces are ubiquitous across natural and engineered systems, including atmospheric aerosols and biological membranes. Thus, gaining a mechanistic understanding of how interfacial properties influence reaction rates is a critical step toward predicting and controlling chemical reactivity, with far-reaching implications for catalysis, atmospheric modeling, biological function, and materials design.In this work, molecular-scale simulations are integrated with coarse-grained kinetic models to quantitatively assess the role of interfacial reactivity in multiphase reaction kinetics. This combined approach reveals how localized surface processes - such as molecular orientation, interfacial thickness, and diffusion - shape the macroscopic observed kinetics. Most studies of interfacial reactivity have focused on aqueous systems, where accelerated reaction rates are typically attributed to dielectric discontinuities or the surface enrichment of reactive solutes. In contrast, organic interfaces have received comparatively less attention. This dissertation focuses on squalene chlorination as a model system for probing chemical reactivity at a non-polar liquid-vapor interface, offering new insight into interfacial mechanisms that emerge independently of electrostatic gradients. Chapter 2 examines squalene chlorination at the air–squalene interface. We find that chlorine reacts at the surface two orders of magnitude faster than in the bulk. This acceleration is driven by a newly identified mechanism, tail spearfishing, in which squalene tails that extend into the gas phase, encounter chlorine with higher probability. Combined with faster interfacial diffusion, these two mechanisms quantitatively explain previously anomalous experimental results in aerosols. Chapter 3 builds on the pure squalene analysis and probes how interfacial reactivity is altered when a long chain alcohol is mixed within the aerosol liquid. Chapter 4 shifts the focus away from direct interfacial reactivity but was motivated by interest in Fenton chemistry at the air–water interface. In an effort to constrain bulk-phase kinetics before introducing interfacial complexity, a unified kinetic model was developed that describes the reaction mechanism across acidic to neutral pH conditions. Taken together, these chapters highlight how detailed molecular and kinetic analysis can reveal the underlying principles governing reactivity across diverse interfacial and bulk-phase environments.