Revealing hidden dynamics via single nanoparticle studies

Nanomaterials constitute the frontier in materials science. Materials with such length scales are typically the minimum units which contain sufficient atoms to display the collective properties which we typically think of a discerning solid-state materials from individual atoms. Characterization techniques, predominantly electron microscopy and tip based methods, have rapidly advance in recent years and now provide routine methods for structural characterization on such length scales. However these methods are fundamentally incompatible with typical environments in which such materials find applications, i.e. in solution under reactive conditions. Herein I seek to develop methodologies based on simple optical microscopy to study individual nano-sized pieces of materials undergoing dynamical restructuring and surface binding events, both to demonstrate the feasibility of the methodology, as well as probe some of the fundamental statistical behavior of such materials under these conditions. Specifically, I focus two predominant systems. The first is a well-studied model system in surface science, that of alkanethiol binding to the surface of individual Ag nanoparticles. This work demonstrates that (surface) structural heterogeneity can influence rates of binding, particularly varying degrees of negative feedback on subsequent binding events depending on the nanoparticle. Secondly, I study galvanic exchange reactions, also on individual Ag nanoparticles. By tuning reactivity of the ionic metal complex inducing replacement, I demonstrate a transition between surface reaction limited and critically driven reaction dynamics. Critical dynamics manifest as distinct temporal offsets between individual nanoparticles in an ensemble undergoing this transition. Such dynamics as demonstrably not the result of structural (or surface structural) heterogeneities, but rather arise due to the stochastic nature of the initial of the critical event at near equilibrium reaction conditions. It is demonstrated that the surface structure does scale the relative concentration at the surface however, which in turn affects the overall ensemble rate, but not the reaction mechanism. Such insight is important from a nanomaterials synthesis prospective, for a detailed understanding of nanoscale corrosion and for accurately model the behavior of nanomaterials transformations