Committee Members:

Prof. Shannon Yee, ME

Prof. John Reynolds, CHEM/MSE

Prof. Jason Azoulay, CHEM/MSE

Prof. Mark Losego, MSE

Prof. Ying Diao, The University of Illinois at Urbana-Champaign

Designing Polymers to Control Electronic and Thermal Transport

Abstract:

Understanding relationships between polymer structure and processing is crucial to create devices with optimal thermal and electronic properties. Thermal conductivity switches, thermoelectrics, pseudocapacitors, and other devices based on polymeric materials offer partial solutions to many problems facing our society, such as energy storage, thermal management, and healthcare. This proposed research seeks to use established chemistry to design new materials with exciting thermal and electronic properties.

In the first research thrust, a series of polymers with reversible Diels-Alder crosslinks are synthesized to investigate how covalent crosslinks impact the thermal conductivity of glassy polymers. The ability to form and break crosslinks and to control the crosslink density with initial polymer design made this material a suitable candidate to be explored as a thermal conductivity switching material. 

The second proposed project utilizes all-donor and donor-acceptor conjugated polymers with chemically removeable side chains. Side chains impart solubility for solution processing, but often limit backbone planarity and charge transport. Following film processing, removal of the side chains densifies the film and increases electronic conductivity. New polymer chemistries are developed to create materials with carboxylate salt and carboxylic acid functional groups after side chain hydrolysis, enabling stronger ionic and hydrogen bonding interactions. Larger dielectric constants and strong interchain interactions after side chain removal is hypothesized to enhance both electronic and ionic conductivity. These redox active polymers can be reversibly doped and de-doped, making them candidates for thermal conductivity switches due to the changing electronic contributions to thermal conductivity. 

Last, polymer-polymer and polymer-solvent interactions lead conjugated polymers to aggregate in solution, especially in non-halogenated solvents. These polymer aggregates form hierarchal structures that span length scales from the atomic to microscale, ultimately impacting the polymer morphology and performance in solid-state and redox applications. This last proposed research thrust focuses on a synthetic approach to design a family of acyclic dioxythiophene (AcDOT) conjugated polymers with varying side chain chemistries and degrees of order. These systematic modifications to the polymer structure and the selected solvent impacts the degree of aggregation and aggregate structures, influencing the observed film morphology, charge transport, and electrochemical properties.