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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2015

Month Degree Awarded

May

First Advisor

Ryan C. Hayward

Subject Categories

Materials Chemistry | Nanoscience and Nanotechnology | Polymer and Organic Materials | Polymer Chemistry

Abstract

This dissertation describes the synthesis of photo-crosslinkable copolymers and their utilization for the fabrication and testing of tunable and responsive one-dimensional (1D) photonic multilayers. Photonic multilayers exhibit structural color due to the interference of incident light at layer interfaces, providing a convenient route towards optically responsive materials that do not rely on potentially light- or oxygen-sensitive chromophore-containing pigments and dyes. A fabrication technique based on sequential spin-coating and crosslinking of photo-crosslinkable polymers is used to assemble tunable and responsive photonic multilayers.

Chapter One introduces the fundamental underlying principles of 1D photonic structures and explores their importance in a variety of areas, including sensors, responsive films, as well as the necessity of their optimization through routes such as the incorporation of nanocomposites for enhanced refractive index. This chapter also details the experimental approach used here for fabricating tunable and responsive 1D photonic multilayers utilizing sequential spin-coating and crosslinking of photo-crosslinkable polymers. Chapter Two describes the use of these multilayer photonic films as thermochromic materials using poly(N-isopropylacrylamide) (PNIPAM) as the low-refractive index, stimulus responsive layers and poly(p-methyl styrene) (PpMS) as the high-refractive index, hydrophobic layers. Temperature is utilized as an analyte to validate this platform as a feasible and flexible approach for the fabrication of a variety of tunable and responsive structures. Building upon the knowledge developed in Chapters 1 and 2, this photonic sensing platform is next expanded to detect additional analytes and further optimize sensor performance by improving reflectance efficiency, response and exploring various multilayer geometries and arrays. Chapter 3 describes the utilization of polymeric photonic multilayers for colorimetric sensing of ionizing radiation. Chapter 4 explores a method of enhancing the reflectance efficiency of multilayers through the incorporation of high refractive index zirconia nanoparticles. The utilization of nanoparticles also enables the fabrication of all-gel multilayers for flexible, potentially mechanochromatic, photonic materials by eliminating the necessity of the high refractive index, but brittle, PpMS. Chapter 5 explores in detail the kinetic response of photonic multilayers with a variety of responsive polymer materials during the swelling and de-swelling phases. Chapter 6 details how this approach can be expanded to create new multilayer geometries, including Bragg filters, as well as multifunctional sensors and arrays on a single substrate. Chapter 7 introduces preliminary work studying the electrochromic response of photonic multilayers. Applied voltage triggers the reversible de-swelling of the responsive layers and subsequently a blue-shift in the wavelength of reflected light. Finally, Chapter 8 provides a summary of this dissertation and proposes future directions for photonic polymer multilayers.

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