Date of Completion

6-5-2018

Embargo Period

12-2-2018

Keywords

Block Copolymers, Self-assembly, Liquid Crystals, Photonic, Bottlebrushes

Major Advisor

Dr. Rajeswari Kasi

Associate Advisor

Dr. Douglas Adamson

Associate Advisor

Dr. Yao Lin

Field of Study

Polymer Science

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Manipulating molecular and supramolecular cooperative interactions to introduce another level of assembly along with block copolymer superstructures has been an important area of research resulting in materials with multiple functionalities. With the aim of attaining hierarchical structures and stimuli responsive multi-functional materials, we introduce a molecularly designed architecture, Liquid Crystalline Brush-like Block Copolymers (LCBBCs), where polymer scaffolds comprising side chain liquid crystalline moieties and brush-like semicrystalline side chains within block or random architecture are introduced. Combination of two architectures can bring the unique conjunction of properties such as i) liquid crystalline order and its stimuli responsive function (magnetic, thermal, light and mechanical stimuli responsive) on the macroscopic scale ii) larger domain sizes (> 100 nm) and faster assembly dynamics of brush-like side chains iii) proximity of order-disorder transition temperature (TODT) and liquid crystalline transition temperature (Tcl) to aid in directed hierarchical self-assembly.

This dissertation focuses on the 1) fundamental understanding of LCBBC self-assembly and phase behavior as a function of composition and molecular weight 2) harnessing stimuli responsive functional properties of cholesteric random copolymeric version of the same architecture to obtain multifunctional photonic elastomeric platform. In first part of dissertation, I describe molecular design-synthesis and characterization of LCBBC architecture comprising norbornene functionalized a) cyanobiphenyl liquid crystalline mesogens with twelve methylene spacer b) semi-crystalline polylactide (PLA) side chains. Morphological variety as a function of composition and dependence of domain spacing on the overall molecular weight is discussed to systematically understand the phase behavior. This architecture exhibits morphology analogous to linear-side chain LC block copolymers and perhaps some characteristics of bottlebrush architecture yielding > 100 nm domain sizes at higher Mn.

In second part, I describe the molecular design-synthesis and characterization of cholesteric random terpolymer architecture to obtain elastomeric photonic platform with shape memory properties. Terpolymer scaffold self-assembles to give a hierarchical structure containing helical cholesteric mesogens along with amorphous microphase segregated domains of PEG brush-like side chains. Synergistic assembly of achiral co-monomers along with cholesteric helices yields tunable photonic reflections as a function of composition. Two-way crosslinking strategy is utilized to obtain patternable elastomeric platform with tunable photonic properties.

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