Interfacial Phenomena and Specific Ion Effects via the Molecular Dynamics Framework

Abstract

Intermolecular interactions are paramount to our understanding of collective physical properties, but present a scientific challenge in that the characteristic length scales of these interactions are below the diffraction limit for direct visualization, and depend on an ensemble of collective molecular motions that are intractable with contemporary quantum mechanics calculations. In such situations molecular dynamics (MD) is a versatile tool, employing empirical potentials to approximate molecular behavior and sample the underlying statistics rigorously. In recent years MD has experienced a renaissance, with sophisticated accelerated sampling techniques and a wide selection of parameterizations. This has allowed for complex environments such as solid-liquid interfaces to be studied in ways previously inaccessible. Interfacial phenomena are particularly important due to their relation to assembly processes, which are relevant to biological complexes and materials development, among other things. The present work explores aqueous response to heterogeneous interfaces for applications in hydrophobic aggregation, ordered self-assembly, and electronic device performance, in each case revealing distinct behaviors when aqueous ion species are exchanged. These specific ion effects have broad ramifications for the resulting physics, and are a crucial part of the sophisticated theoretical framework needed to predict outcomes a priori. Toward this goal, MD provides a route to explore underlying mechanisms, quantifying solution structure and applying macroscoping theory where relevant to connect microscopic phenomena with macroscopic outcomes.