Molecular perspective and engineering of thermal transport and thermoelectricity in polymers

Abstract

Designing polymers with desirable thermal or thermoelectric properties has been a great goal in the field of organic functional materials. This is widely considered challenging because polymers manifest complicated transport characteristics due to their intertwined molecular chains, complex intra- and inter-molecular interactions, and strong heterogeneities in both morphology and pathways of primary energy carriers. These molecular- and nano-scale attributes regulate energy transport and conversion, leading to low bulk-level thermal conductivity and moderate thermoelectric energy conversion performance. Polymers with extreme and controllable thermophysical properties hold the potential to advance many thermal management and renewable energy technologies. The past decade has witnessed significant progress on this topic, owing to the advances in micro-, nano-, and molecular-scale engineering that have created polymers with metal-like thermal conductivity for thermal management technologies and polymers with high charge carrier density for thermoelectric applications. This review focuses on molecular perspective and engineering in two key areas: thermoelectric properties in conducting polymers and thermal transport in polymers with phonons as the dominant energy carrier. The review begins with a theoretical explanation of charge and thermal transport in polymers from a molecular and mesoscale perspective. It reviews thermoelectric polymer synthesis and modification methods for increasing thermoelectric efficiency. The later section of the review surveys molecular engineering efforts in optimizing thermal transport in polymers with phonons as the dominant energy carrier and discusses the interrelated charge and thermal transport in conducting polymers. We also summarize recent efforts to study the dynamic control of thermal and thermoelectric properties of polymers using external stimuli. Finally, we discuss some outstanding challenges and potential future directions.