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.