Interactions and Assemblies of Polymeric Materials and Colloidal Nanocrystals

Our need to reduce global energy use is well known and without question, not just from/nan economic standpoint but also to decrease human impact on climate change. Emerging/nadvances in this area result from the ability to tailor-make materials and energy-saving/ndevices using solution–phase chemistry and deposition techniques. Colloidally/nsynthesized nanocrystals, with their tunable size, shape, and composition, and unusual/noptical and electronic properties, are leading candidates in these efforts. Because of/nrecent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has/nexpanded to now include metals, semiconductors, magnetic materials, and dielectric/nmaterials. For a variety of applications, an active layer composed of a thin film of/nrandomly close-packed nanocrystals is not ideal for optimized device performance; here,/nthe ability to arrange these nano building units into mesoporous (2 nm < d < 50 nm)/narchitectures is highly desirable. Given this, the goal of the work in this dissertation is to/ndetermine and understand the design rules that govern the interactions between ligand-stripped/nnanocrystals and polymeric materials, leading to their hierarchical assembly into/ncolloidal nanocrystal frameworks. I also include the development of quantitative, and/nnovel, characterization techniques, and the application of such frameworks in energy/nefficiency devices such as electrochromic windows./nUnderstanding the local environment of nanocrystal surfaces and their interaction/nwith surrounding media is vital to their controlled assembly into higher-order structures./nThough work has continued in this field for over a decade, researchers have yet to/nprovide a simple and straightforward procedure to scale across nanoscale material/nsystems and applications allowing for synthetic and structural tunability and quantitative/ncharacterization. In this dissertation, I have synthesized a new class of amphiphilic block/ncopolymer architecture-directing agents based upon poly(dimethylacrylamide)-b-poly(/nstyrene) (PDMA-b-PS), which are strategically designed to enhance the interaction/nbetween the hydrophilic PDMA block and ligand-stripped nanocrystals. As a result,/nstable assemblies are produced which, following solution deposition and removal of the/nblock copolymer template, renders a mesoporous framework. Leveraging the use of this/nsacrificial block copolymer allows for the formation of highly tunable structures, where/ncontrol over multiple length scales (e.g., pore size, film thickness) is achieved through the/njudicious selection of the two building blocks. I also combine X-ray scattering, electron/nimaging, and image analysis as novel quantitative analysis techniques for the physical/ncharacterization of the frameworks./nLast, I demonstrate the applicability of these porous frameworks as platforms for/nchemical transformation and energy efficiency devices. Examining the active layer in an/nelectrochromic window, I show a direct comparison between, and improved performance/nfor, devices built from both randomly close-packed nanocrystals and those arranged in/nmesoporous framework architectures. I show that the framework also serves as a scaffold/nfor in-filling with a second active material, rendering a dual–mode electrochromic device./nThese results imply that there may exist a broad application space for these techniques in/nthe development of ordered composite architectures.

Advisor: Helms, Brett A
Xu, Ting