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Document Type

Campus-Only Access for One (1) Year

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

Year Degree Awarded

2019

Month Degree Awarded

February

First Advisor

Professor Sankaran Thayumanavan

Subject Categories

Materials Chemistry | Organic Chemistry | Polymer Chemistry

Abstract

Amphiphilic self-assembly has gained a lot of interest in both academic and industrial fields. Amphiphiles have a unique ability to self-assemble in water, providing a range of nanosized materials of various morphologies. Many efforts have been dedicated to developing responsive amphiphilic assemblies by introducing responsive characteristics into the amphiphile building blocks. Responsive assemblies have been utilized in many promising applications such as targeted drug delivery systems, smart sensors, and electronic devices. Here, we reported four different types of responsive assemblies created via the incorporation of different responsive groups either at the material’s surface or interface.

To achieve the responsive characteristics at the surface of the assemblies, we designed an amphiphilic homopolymer capable of self-assembly in water to form micelle-like aggregates. The polymer was designed in such a way that the amine functional groups are presented at the surface for further surface modifications. Organic semiconductor molecules were functionalized onto the spherical polymeric micelle-like assemblies and their response in charge transport was analyzed. We utilized the simple spherical micelle-like assemblies as a scaffold to provide isotropic structure in organic semiconductors. Three key findings in this work include 1) the spherical structure to provide isotropic charge transport, 2) the maintenance of charge transport, and 3) the improvement in thermal stability. Furthermore, fluorescent molecules were also functionalized to the spherical micelle to yield fluorescent particles that demonstrated fluorescent enhancement compared to their small molecules counterpart. The mechanism of the emission enrichment was deeply investigated and discussed in the later work.

The responsive characteristics at interfaces of amphiphiles were also included in this dissertation. Alternatively to micelle-like assemblies, responsive vesicles were prepared from amphiphilic polymers with three components including hydrophilic, hydrophobic and pH-responsive segments. The positions of the pH-responsive units were optimized to achieve the ability of controlled release. Positions of the responsive groups were varied in the hydrophilic and hydrophobic interface and the effect of the position was examined through kinetic studies of molecular guest release and morphology transitions. Last but not least, the responsive oligomeric amphiphiles were designed to assemble at liquid crystal and water interfaces. Using responsive amphiphiles at such an interface allows the potential to greatly amplify a nanoscopic change into a macroscopic one due to the amphiphile’s response to an applied stimulus. We aimed to develop such a responsive system demonstrating liquid crystal reorganization due to a nanoscopic change of the triggerable amphiphiles interfacial orientation. Our system demonstrates macroscopic changes in liquid crystal optical properties which could contribute to the development of highly sensitive analysis tools.

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