Prof. David Cahill, Univ. of Illinois, Urbana-Champaign - Extremes of Heat Conduction in Molecular Materials

Abstract: Thermal conductivity is a basic and familiar property of materials that plays a pivotal role in a broad range of topics in energy science and engineering systems. In this talk I will emphasize recent examples of extreme behavior—and behavior under extreme conditions—in polymers and molecular solids. Our measurements of heat conduction in novel materials are enabled by variety of ultrafast optical pump-probe metrology tools developed over the past decade. At the low end of the thermal conductivity spectrum, fullerene derivatives display the lowest thermal conductivity ever observed in a fully dense solid, comparable to the conductivity of disordered layered WSe2 and only twice that of air. Extremes of high pressures (up to 60 GPa) allow us to continuous change the strength of molecular interactions in glassy polymers and test theoretical descriptions of the mechanisms for heat conduction. The thermal conductivity of aligned, crystalline and liquid crystalline polymer fibers can be surprisingly high, comparable to that of stainless-steel.  The dominate carriers of heat appear to be longitudinal acoustic modes with lifetimes dictated by anharmonic processes.

Biography: Prof. Cahill joined the faculty of the University of Illinois at Urbana-Champaign in 1991 after earning his Ph.D. in condensed matter physics from Cornell University in 1989, and working as a postdoctoral research associate at the IBM Watson Research Center. In 2005, he was named Willett Professor of Engineering and was appointed Head of the Department of Materials Science and Engineering in 2010. His research program focuses on developing a microscopic understanding of thermal transport at the nanoscale; the development of new methods of materials processing and analysis using ultrafast optical techniques; and advancing fundamental understanding of interfaces between materials and water. He received the Peter Mark Memorial Award from the American Vacuum Society (AVS); is a fellow of the AVS, American Physical Society (APS) and Materials Research Society (MRS); and is currently chair of the Division of Materials Physics of the APS.