The Controlled, Site-Isolated Synthesis of Polyelemental Nanostructures in Polymer Nanoreactors


The Controlled, Site-Isolated Synthesis of Polyelemental Nanostructures in Polymer Nanoreactors Pengcheng Chen Polyelemental nanoparticles are an attractive class of materials due to their potential applications, which span the fields of catalysis, plasmonics, electronics, magnetics, targeted drug delivery, and bio-imaging. However, conventional synthetic methods for such structures are limited, especially when the number of elements exceed three. Moreover, the challenge of systematically exploring polyelemental nanoparticles is daunting, due to the vast compositional and structural parameter space that must be examined to adequately elucidate the governing composition and size structure-property relationships. This thesis focuses on the development of methodology for synthesizing polyelemental nanoparticles in a manner that allows for systematic control over structure and composition and is amenable to high throughput screening. Chapter One begins with an overview of polyelemental nanoparticles and their importance in chemistry and materials science. State-of-the-art synthetic methods for polyelemental nanostructures are reviewed, along with the applications of such materials in the catalysis field. Chapter Two describes the concept of scanning probe block copolymer lithography (SPBCL), which allows one to generate metal ion-containing polymer nanoreactors in order to synthesize individual nanoparticles. Using five elements (Au, Ag, Co, Cu, and Ni) as a model system, SPBCL was used to synthesize and study all combinations of the five elements at a fixed particle size. This work is important since it sets the stage for using SPBCL as a novel tool for rapidly synthesizing and exploring entire new classes of polyelemental nanoparticles, and points toward the ability to rapidly define their structures and corresponding physical and chemical properties. Chapter Three further investigates the formation pathway of polyelemental nanoparticles in nanoreactors. A three-stage nucleation and growth process has been identified as central to particle formation. Chapter Four reports a library of novel SPBCL-synthesized nanoparticles composed of up to seven elements and four phases. Design rules for engineering the configuration of interfaces in polyelemental heterostructured nanoparticles are enumerated. The power of these rules was demonstrated by synthesizing an unprecedented tetra-phase nanoparticle with a six-interface architecture. Given the importance of heterostructured materials in catalysis and energy, these design rules provide a way of engineering polyelemental systems with unprecedented complexity and control. Chapter Five describes the scale-up synthesis of polyelemental nanoparticles on centimeter-scale substrates with cantilever-free scanning probe techniques. Nanoparticle arrays with a size gradient are used to demonstrate how this technique can be used for particle library generation and high-throughput catalyst screening. Finally, Chapter Six provides an outlook on polymer nanoreactor-mediated nanoparticle synthesis and highlights several future research directions. ______________________________________ Thesis Advisor: Prof. Chad A. Mirkin

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