Date of Award

Spring 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Dr. Jason D. Azoulay

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Dr. Xiaodan Gu

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Dr. Jeffrey S. Wiggins

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Dr. Sarah E. Morgan

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Dr. Derek L. Patton

Committee Member 5 School

Polymer Science and Engineering

Abstract

Widespread efforts in scientific and engineering disciplines over the last half century have led to the advancement of organic-based electrical conductors, including allotropes of carbon, neutral radicals, and charge transfer salts. Conducting polymers (CPs) are a dominant class of organic conductors for coatings, composites, textiles, sensors, and electronic applications requiring light-weight structures and the integration of multifunctional properties. Conventional CPs largely derive their conductivity from doping; a process reliant on harsh redox and charge-transfer reactions that improve the conductivity to levels suitable for various applications. The doping process often leads to transient properties subject to degradation, limiting their potential application in emerging technologies. In this dissertation, we demonstrate a new class of charge-neutral donor–acceptor CPs rich in charge carriers and impressive intrinsic conductivity (without doping) from thermal population of electrons into the conduction band at room temperature. Control of room-temperature conductivity spanning over several orders of magnitude was established through precise bandgap engineering, careful manipulation of the ground state electronic structure, systematic control of solid-state microstructures, which ultimately yield the discovery of unique electronic, optical, spin, thermoelectric (TE), and magnetic behavior previously unrealized in undoped polymeric systems.

Aimed at understanding and developing high performing intrinsically CPs, we start with reviewing the characteristics of conventional organic conductors, emphasizing the mechanism for charge carrier generation and associated limitations for doped CPs. We exhaustively summarize the practical strategies of narrowing bandgaps for free charge carrier generation and promoting intra- and interchain charge transport (Chapter I). Armed with these design guidelines, we synthesize and systematically investigate nine different polymers in three distinct systems through backbone engineering for donor moieties (P1–P3), subtle structural modifications (P4–P6), and side-chain engineering (P7–P9). Various building blocks and effective molecular design rules for improving intrinsic conductivity are identified in this process, with the improvement in conductivity spanning four orders of magnitude from 10–7 (P3) to 10–3 S cm–1(P9) (Chapter II). While conductivity can be systematically modulated via molecular engineering, the morphological control through unique processing techniques leads to distinct fibrous microstructures and an unprecedented conductivity of 8 S cm–1 (P10) (Chapter III). Building on the high performing CPs developed in Chapter II and III, Chapter IV demonstrates their applications as novel TE materials with one of the largest power factors (S >10 μW m–1 K–2) reported among nontraditional CP-based TE materials. In Chapter V, the potential application of CPs (P10 and P14) as effective conductive matrices and noncovalent dispersants for single-walled carbon nanotube (SWCNT) composites were explored. The CP/SWCNT composites were engineered to achieve a remarkable conductivity of 180 S cm–1 at 20 wt% SWCNT loading by forming a well-dispersed P14/SWCNT conductive network, utilizing a highly conductive CP matrix (P10).

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