Date of Completion

8-23-2013

Embargo Period

8-23-2015

Keywords

block copolymer, liquid crystal, photonic, nanoporous materials, directed self-assembly

Major Advisor

Prof. Rajeswari M. Kasi

Associate Advisor

Prof. Yao Lin

Associate Advisor

Prof. Douglas H. Adamson

Field of Study

Chemistry

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

One of the fascinating subjects in scientific research is the creation of self-assembled smart functional systems with hierarchical orders mimicking functional biological molecule such as spider silk, tendon, bone, proteins, and lipids. Multi-functional properties associated with these hierarchical structures are partly due organization with outstanding precision at discrete length scales, which ranges from molecular level (nanometer) to macroscopic (micrometer) length. Among various synthetic self-assembly process, the self-organization of liquid crystalline block copolymers (LCBCPs) have attracted much interest because of their abilities to form hierarchical structures consisting of microphase separated domains from block copolymers and anisotropic mesophase ordering from LC mesogen. Beyond linear LCBCP architecture, there is increasing interest in exploiting nonlinear topologies comprising dendritic, hyper-branched and brush-like moieties within BCPs. In all cases, the branched architecture of the polymer framework imparts extraordinary self-assembled structure compared to their linear-polymer counterparts and studying the interplay of competing self-assembly process will be crucial to create new smart material for various applications. This dissertation focus on exploiting copolymer architecture with LC and brush-like side-chain moieties for different types of smart materials: 1) hierarchically self-assembled photonic materials and 2) directed large area self-assembled nano-template.

In first part of dissertation, I describe the synthesis and characterization of side-chain copolymers comprising (1) cholesteryl mesogen with nine methylene spacer and (2) semicrystalline poly(ethylene glycol) (PEG) resulting in liquid crystalline brush block copolymers (LCBBC) and liquid crystalline random brush copolymer (LCRBC) architecture. The difference in copolymer architecture leads to significant distinction in thermal, mesomorphic and optical properties of resulting copolymers. In case of LCBBC morphologies studies reveal various hierarchical structures as a result of the interplay between the microphase segregation in brush-like macromolecules and the LC order wherein the microphase segregated domains strengthen the liquid crystalline order and thereby prevent the formation of cholesteric mesophase. In sharp contrast, synergistically self-assembled hierarchical mesostructures in the LCRBC architecture engenders photonic properties.

In second part of this dissertation, I have exploited side-chain copolymers with specifically designed functional groups for nano-template applications. These copolymers consist of polynorbornene backbone with polylactide (PLA) and cyanobiphenyl mesogen with methylene spacer as side chain functional groups. By molecular engineering PLA block length and spacers that connect the cyanobiphenyls to polynorbornene backbone microphase segregated morphologies are created. Furthermore, utilizing the inherent magnetic susceptibility of cyanobiphenyl moieties results in large area alignment of nano-templates. Overall, control over self-assembly is critical towards creating nano-templates for various applications.

Download

Share

COinS