UC Berkeley

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.