Synthesis and characterization of core/shell hydrogel nanoparticles and their application to colloidal crystal optical materials

This dissertation describes the use of spherical core/shell type micro- and nanoparticles as building blocks for the fabrication of colloidal crystals. The polymer component used in all of the projects that are described herein is poly-N-isopropylacrylamide (pNIPAm). The polymeric identity of particles composed of this soft, hydrogel material, which is also thermoresponsive, contributes to the self-assembly of such particles to form ordered structures. Chapter 2 examines a characterization technique using fluorescence resonance energy transfer (FRET) to investigate the structure of particles that possess a core/shell topology. Chapters 4-6 investigate strategies to impart both hard (dense core) and soft (flexible shell) properties to the particles by using styrene as the main component in a copolymer synthesis with pNIPAm (pS- co-NIPAm particles). The resulting crystal assemblies, which could be formed by simple drying procedures, were demonstrated to be robust and their application as processable, photonic inks is also investigated. Chapter 7 examines the ability to crosslink these crystals together by simple heating methods to produce robust films, and the optical properties of these crystal films could be tuned by simple rehydration. Chapters 3 and 5 examine the synthesis and self-assembly strategies of core/shell particles using the properties of pNIPAm shell layers that have been added to different types of core particles (silver or pS-co-NIPAm) for the purposes of fabricating colloidal crystals using thermal annealing procedures. Chapter 8 explores the use of silver particles as tracers for the characterization of colloidal crystals composed of thermally annealed colloidal crystals composed of pNIPAm hydrogel particles.