Our need to reduce global energy use is well known and without question, not just from an economic standpoint but also to decrease human impact on climate change. Emerging advances in this area result from the ability to tailor-make materials and energy-saving devices using solution–phase chemistry and deposition techniques. Colloidally synthesized nanocrystals, with their tunable size, shape, and composition, and unusual optical and electronic properties, are leading candidates in these efforts. Because of recent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has expanded to now include metals, semiconductors, magnetic materials, and dielectric materials. For a variety of applications, an active layer composed of a thin film of randomly close-packed nanocrystals is not ideal for optimized device performance; here, the ability to arrange these nano building units into mesoporous (2 nm < d < 50 nm) architectures is highly desirable. Given this, the goal of the work in this dissertation is to determine and understand the design rules that govern the interactions between ligand-stripped nanocrystals and polymeric materials, leading to their hierarchical assembly into colloidal nanocrystal frameworks. I also include the development of quantitative, and novel, characterization techniques, and the application of such frameworks in energy efficiency devices such as electrochromic windows.
Understanding the local environment of nanocrystal surfaces and their interaction with surrounding media is vital to their controlled assembly into higher-order structures. Though work has continued in this field for over a decade, researchers have yet to provide a simple and straightforward procedure to scale across nanoscale material systems and applications allowing for synthetic and structural tunability and quantitative characterization. In this dissertation, I have synthesized a new class of amphiphilic block copolymer architecture-directing agents based upon poly(dimethylacrylamide)-b-poly( styrene) (PDMA-b-PS), which are strategically designed to enhance the interaction between the hydrophilic PDMA block and ligand-stripped nanocrystals. As a result, stable assemblies are produced which, following solution deposition and removal of the block copolymer template, renders a mesoporous framework. Leveraging the use of this sacrificial block copolymer allows for the formation of highly tunable structures, where control over multiple length scales (e.g., pore size, film thickness) is achieved through the judicious selection of the two building blocks. I also combine X-ray scattering, electron imaging, and image analysis as novel quantitative analysis techniques for the physical characterization of the frameworks.
Last, I demonstrate the applicability of these porous frameworks as platforms for chemical transformation and energy efficiency devices. Examining the active layer in an electrochromic window, I show a direct comparison between, and improved performance for, devices built from both randomly close-packed nanocrystals and those arranged in mesoporous framework architectures. I show that the framework also serves as a scaffold for in-filling with a second active material, rendering a dual–mode electrochromic device. These results imply that there may exist a broad application space for these techniques in the development of ordered composite architectures.
|Advisor:||Helms, Brett A., Xu, Ting|
|Commitee:||Francis, Matthew B., Gronsky, Ronald|
|School:||University of California, Berkeley|
|Department:||Applied Science and Technology|
|School Location:||United States -- California|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Subjects:||Polymer chemistry, Nanoscience, Materials science|
|Keywords:||Block copolymer self assembly, Colloidal nanocrystals, Electrochromic windows, Electron imaging, Nanocrystal surfaces, X-ray scattering|
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