Molecular Phononics: Understanding and Controlling Thermal Transport in Polymers from Single Molecules to Micro/Nanoscale Fibers

Managing heat flow in polymers and exploiting it in real-world devices has long been a central goal in organic materials research. The challenge stems from polymers’ complex thermal behavior such as intra- and intermolecular interactions and heterogeneity in morphology and phonon transport pathways. Polymers with extreme, tunable thermal properties could unlock advances in thermal management, flexible electronics, and renewable energy technologies.

In this talk, I will present our efforts to understand and control phonon transport in polymers across scales from single molecules to mesoscopic structures such as micro/nanofibers. At the molecular and atomic limits, a key hurdle is developing experimental tools with ultrahigh spatial stability and thermal sensitivity to resolve picowatt-level heat currents where coherent transport is expected for thermal phonons. I will present a custom, high-resolution twin-tip scanning thermal microscopy (SThM) platform that enables real-time, simultaneous measurements of phonon and electron transport in single-molecule and atomic junctions. Using this platform, we directly observe destructive phonon interference at room temperature in single-molecule junctions made of para- and meta-connected oligophenylene-ethynylene trimers (Nature Materials, 24, 258–1264 (2025)). Molecular dynamics simulations reproduce both the magnitude of conductance and the suppression of thermal transport due to destructive interference, tracing it to canceling phonon modes along the kinked aromatic backbone. These results confirm long-standing predictions and show that coherent phonon phenomena can persist at room temperature when confined to single-molecule dimensions.

At the mesoscopic scale, we developed a separate low-cost picowatt-resolution platform (Sensors and Actuators A, 388, 116494 (2025)) that requires no complex nanofabrication to study thermal transport in light-responsive polyazobenzene micro/nano fibers. We find an unexpectedly large temperature coefficient of thermal conductivity that tracks the polymer’s glass transition in both the trans and cis states. I will discuss plausible molecular-scale mechanisms, supporting simulations, and opportunities to harness externally stimulable polymers for thermal management applications.