题 目：Thermal Transport in Amorphous Polymers, Conducting Polymers, and Polymer Fibers
报告人：Prof. Liu Jun，（Department of Mechanical and Aerospace Engineering, North Carolina State University, NC27695，USA）
Thermal and elastic properties of polymers are critical engineering considerations for flexible substrate, interfacial binders, and encapsulation layers for electronics. Thermal transport in amorphous polymers is generally limited by structural disorder and weak interactions between chains. Typically glassy polymers have a universally low thermal conductivity ≈0.2 W m-1 K-1. In this talk, I will start with thermal transport in amorphous polymers and show our recent measurements on the thermal conductivity, heat capacity, and elastic constants of water-soluble polymers and one of their blends. The thermal conductivity correlates positively with the sound velocities, in agreement with the prediction of Cahill-Pohl minimum thermal conductivity model. Then I will show thermal transport and elastic constants measurements of conducting polymer PEDOT:PSS films. We find the changes of thermal conductivity as a function of electrical conductivity in PEDOT:PSS films are consistent with the Wiedemann-Franz law and the Sommerfeld value of the Lorentz number. Last, I will talk about the anisotropic thermal transport in polymer fibers, especially in the radial direction. Polymer fibers with different molecular arrangements (crystalline, liquid crystalline, and amorphous)wereplastically deformed and wasthen measured its thermal conductivity in the radial direction. Thermal conductivity decreases with increasing strains for crystalline and liquid crystalline PE and PBO fibers and remains constant for PMMAfibers. The combination of structural disorder and phonon focusing effects produces a thermal conductivity in deformed PE and PBO fibers that is lower than amorphous PMMA. Those findings could enable better understanding of thermal transport in polymeric material.
Dr. Jun Liu is an assistant professor in Department of Mechanical and Aerospace Engineering at NC State. Prior to that, he was a postdoctoral research associate in Materials Science and Engineering Department at University of Illinois at Urbana-Champaign. He received his B.E. in thermal engineering from Huazhong University of Science and Technology (Wuhan, China) in 2008 and Ph. D. in Mechanical Engineering from University of Colorado at Boulder in 2013. He was honored Outstanding Dissertation Award by College of Engineering at CU-Boulder in 2013. His research interests include atomistic simulation and ultrafast-laser characterization of thermal transport, thermal energy conversion and storage, thermal management of microelectronics, and nanoscale thermal transport phenomena in advanced materials.