RESPONSIVE NANOSTRUCTURE MORPHOLOGIES THROUGH DYNAMIC ASSEMBLY OF BRANCHED FUNCTIONAL POLYMERS

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Lee, Hansol
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http://hdl.handle.net/1853/65092
Abstract
Generating responsive polymeric nanostructures is critical for emerging applications in drug delivery, bio-sensing, bio-imaging, self-healing coatings, and soft robotics. Branched polyelectrolytes are promising candidates for designing unique responsive polymeric nanostructures with diverse morphologies and functionalities due to their intrinsic responsive nature depending on solvent conditions and distinct phase behavior. A grand challenge in this field is to precisely control the interactions and molecular organization of branched polyelectrolytes and to program their self-assembly into complex morphologies. Therefore, the primary goal of this research is to establish a fundamental understanding for generating nanostructures with responsive morphology and properties by controlling the assembly of branched polyelectrolytes. Firstly, the responsive properties of amphiphilic hyperbranched polyelectrolytes with variable peripheral chemical composition were investigated at different interfaces. We found that the monolayer films of thermo-responsive hyperbranched polyelectrolytes with asymmetric chemical composition exhibited unusual morphological transformation from disk to ridge-like structures upon surface compression. Secondly, we studied the effect of highly mobile thermo-responsive macro-cations, ionically linked to terminal ionic groups on the assembly of hyperbranched polyelectrolytes. The macrocations can hop between terminal ionic groups, creating mobile coronas which can contribute to obtaining diverse morphological variation under changing assembling condition. Both studies demonstrate that concurrent control on the surface morphology, surface mechanical property distribution and surface potential distribution of the monolayer films of the thermo-responsive hyperbranched polyelectrolytes can be achieved by varying peripheral chemical composition or adjusting deposition conditions. Thirdly, the assembly of star-shaped oligomeric ionic liquids containing inorganic cores and organic shells with alkyl substituents of variable lengths was investigated. The length of hydrophobic alkyl substitutes significantly affects the self-organization in aqueous media and on a solid surface as well as the thermal and ion transport properties of the oligomeric ionic liquids. Lastly, shape-persistent, highly conductive ionogels were produced by using hyperbranched poly(ionic liquid)s as binding functional components with cellulose nanocrystals. The resulting composite ionogel materials showed a unique combination of both enhanced mechanical and ion transport properties. Thus, the ionogel materials suggests a novel approach to resolve mechanical stability vs ionic conductivity dilemma for developing high-performance electrolyte materials. Overall, this dissertation provides novel approaches to preparing finely tuned polymer nanostructures with responsive morphology and properties by modulating the assembly of branched polyelectrolytes. This work also offers promising potential of branched polyelectrolytes in the development of novel composite materials with tunable morphologies and unique smart functions.
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2021-07-28
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