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THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING
GEORGIA INSTITUTE OF TECHNOLOGY
Under the provisions of the regulations for the degree
DOCTOR OF PHILOSOPHY
on Wednesday, September 5, 2018
4:00 PM
in MRDC 3515
will be held the
DISSERTATION PROPOSAL DEFENSE
for
Connor Callaway
"Multiscale Modeling of Multicompartment Micelle Nanoreactors: Influence of Polymer Architecture on Structural Variation and Transport Behavior"
Committee Members:
Dr. Seung Soon Jang, Advisor, MSE
Dr. Zhiqun Lin, MSE
Dr. Paul Russo, MSE
Dr. Donggang Yao, MSE
Dr. Christopher Jones, ChBE
Abstract:
Efficient reaction design forms an important foundation of many processes in modern chemistry. Reaction optimization has far-reaching effects that greatly improve many other facets of polymer manufacturing, pharmaceutical production, and related industries. In particular, a field of growing interest during the past century is that of immobilized molecular catalysis. This topic holds great potential due to its combination of the best strengths of both homogeneous and heterogeneous catalysis. By allowing for high selectivity and reaction rates traditionally achieved by homogeneous catalysis while still yielding the excellent separability offered by heterogeneous catalysis, this field presents an opportunity to leverage the advantages of both techniques. Despite the strengths of immobilized molecular catalysis, however, systems containing multiple tandem non-orthogonal reactions (i.e., reactions which have the potential for mutual interference) still encounter difficulties. In extreme cases, a particular step of the multistep reaction may even be incompatible with another species present in the system; in such a case, the catalyzing agent could suffer drastically reduced efficacy or cease to function altogether.
A potential solution to these obstacles arises in a field of study which has been the subject of growing academic interest in recent years – namely, that of multicompartment micelles. These systems offer separate molecular “chambers” in which each of the non-orthogonal reactions can take place, allowing for one-pot synthesis and tandem catalysis. Micelles are, of course, well studied in chemistry; indeed, the multicompartment micelle (MCM) is simply an extension of the traditional idea. It is well known that a typical micelle is generally composed of polymers which have hydrophilic and hydrophobic portions. MCMs, then, are composed of polymers of three or more distinct portions; a common example results from triblock copolymers containing hydrophilic, lipophilic, and fluorophilic (HLF) blocks. For a proper choice of solvent, solutions of these polymers thus self-assemble into micellar structures containing three or more regions of microphase separation. By introducing immobilized catalysts into MCM-containing systems, it is possible to create a micelle nanoreactor. Because of the multicompartmental nature of the micelles in the system, it is possible to introduce different immobilized catalysts within each region of the MCM, thereby creating distinct catalytic regions within the structure that support simultaneous non-orthogonal reactions in the same chamber while still achieving high reaction rates and easy separability. The micelle nanoreactor (MNR) thus presents an elegant solution to many of the challenges facing immobilized molecular catalysis science.
It is natural to expect that the particular structural morphology of the micelles formed by a given polymer will in turn affect their utility in MNR applications. By extension, the particular architecture of the polymers selected for the formation of MCMs will have a marked effect on the performance of the resultant MNR system. For example, even if the species which define the different regions of solvophilicity of the polymer are held constant, variations in the sequence, lengths, and length ratios of the respective blocks can lead to significant morphological changes in the resultant MCMs. Such changes can then lead to diminished catalyst effectiveness (e.g., due to decreased extent of compartmentalization) or less desirable reactant and product transport (leading to reduced reaction rates). Therefore, proper design of MCM systems for use in MNR applications requires complete understanding of how to control the polymer architecture and, consequently, the micelle structure. A systematic study of the effects of the relevant variables is, however, made difficult in experiment due to the time-consuming preparation and reactions involved. Computational techniques offer a more economical avenue for the study of large systems such as these, as they allow for direct analysis of the MCM structure without the need for structural synthesis.
Considering all of these factors, the present work aims to study the effects of polymer architecture and composition on the structure of the resulting self-assembled MCMs and, as a consequence, on the transport characteristics of reactant and product species through the micelles. Preliminary studies on this system have already been carried out. The foundation for the principal focus of this study lie in the development of a robust methodology for determining the miscibility of polymer species and a study of micelle structure tunability as a function of the lengths and length ratios of an HLF triblock copolymer system, both of which have been completed. Having now laid the groundwork, future work will focus on the introduction of reactants, products, and potentially catalysts into the MCM systems in order to directly study the effectiveness of such a system for MNR purposes.
