THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Tuesday, July 13th, 2021

1:00 PM

via

BlueJeans Video Conferencing

https://bluejeans.com/516236002/5202

will be held the

DISSERTATION DEFENSE

for

Hansol Lee

"Responsive Nanostructure Morphologies through Dynamic Assembly of Branched Functional Polymers"

Committee Members:

Prof. Vladmir Tsukruk, Advisor, MSE

Prof. Valeria Milam, MSE

Prof. Zhiqun Lin, MSE

Prof. Blair Brettmann, ChBE/MSE

Prof. Andrei Fedorov, ME

Abstract:

Responsive polymeric nanostructures have received considerable attention due to their abilities to change their morphologies by responding to external stimuli, and potential applications in drug delivery, bio-sensing, bio-imaging, self-healing coatings, and soft robotics. Polymers containing ionic groups, such as polyelectrolytes and poly(ionic liquid)s, are promising candidates for designing responsive polymeric nanostructures with diverse morphologies and functionalities. However, it is challenging to program the formation of complex morphologies with adaptive and switchable properties by using polyelectrolytes and poly(ionic liquid)s with simplistic linear architecture. This research addresses this issue by introducing variable macromolecular architecture, functionality, and environmental conditions into the assembly of polyelectrolytes and poly(ionic liquid)s.

The ultimate goal of the research is to establish fundamental predictable routes for generating nanostructures with pre-programmed and responsive morphology and properties by controlling the assembly of branched polyelectrolytes. Accordingly, in the first place, the role of chain architecture and chemical composition on the assembly, interfacial behavior, and complex interfacial morphologies of branched polyelectrolytes is examined. We studied the responsive properties of amphiphilic hyperbranched polyelectrolytes with variable peripheral chemical composition at air/water interface and in Langmuir-Blodgett monolayer. We found that thermo-responsive hyperbranched polyelectrolytes with asymmetric chemical composition showed unusual morphological transformation from disk to ridge-like structures upon compression, which is different from that of traditional amphiphilic block copolymers. Not only morphology and but also mechanical response of their monolayers can be tuned by changing temperature and surface pressure. Secondly, we studied the effect of highly mobile thermo-responsive macro-cations, ionically linked to terminal ionic groups on dynamic assembly of hyperbranched polyelectrolytes. The macrocations can hop between neighboring terminal ionic groups, generating mobile coronas which can contribute to obtaining diverse morphological variation under changing assembling conditions. Thirdly, the assembly of star-shaped oligomeric ionic liquids containing inorganic cores and organic shells with alkyl substituents of variable lengths is investigated. The length of alkyl substitutes significantly affects the self-organization in aqueous media and on a solid surface with tunable surface morphology and adhesion. Finally, we utilized hyperbranched poly(ionic liquid)s as a binding functional component to fabricate functional composite materials. Multiple functionalities of hyperbranched poly(ionic liquid)s enable the generation of multiple physical interactions with other components of the composite materials.  The resulting composite ionogel materials show both enhanced mechanical and ion transport properties.

Overall, this work offers novel approaches to preparing finely tuned polymer nanostructures with responsive morphology and properties. This work helps to establish a systematic, transformative understanding, and construction of component-structure-property relationships for branched polyelectrolytes. In addition, the development of functional composites with novel mechanical performance and conductivity by exploiting hyperbranched poly(ionic liquid)s meets challenging requirements for materials in energy storage and conversion applications, potentially discovering next-generation electrolyte materials.