Study of Thermal Transport in Single Oligomer and Polymer Chains

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The principal goal of this research project is to experimentally study how heat is transported through single molecular chains. In contrast to bulk materials, researchers have only been able to make theoretical calculations regarding the flow heat through individual molecules, which include the surprising prediction that the resistance to heat flow is independent of the length of the molecule. Direct experimental measurements of the heat flow in single molecules have remained impossible due to the lack of appropriate instrumentation techniques to stably hold or confine single molecules and record the minute heat currents with sufficient resolution. In this proposal recent, groundbreaking experimental advances in picowatt-resolution calorimetry, high-resolution temperature measurements and experimental platforms will be used to tackle these challenging measurements with a systematic, experimental approach. In addition to the technical work, the proposal also incorporates extensive outreach activities to engage undergraduate and graduate students as well as underrepresented minorities in neighboring communities in research.Thermal transport in single molecules and polymer chains, excellent approximations of one-dimensional systems, is of great current interest. Theoretical and computational studies, starting with Fermi, Pasta and Ulam in the 1950s, suggest that Fourier?s law is generally not valid for one-dimensional chains and imply the existence of a length-dependent, divergent thermal conductivity. To test these predictions detailed experimental measurements on single one-dimensional chains are essential to answer the following questions: What is the thermal conductance of single polymer molecules, how does it depend on the chain length and does the thermal conductivity diverge for all 1-dimensional systems? Can the thermal conductivity of single polymer molecules be modulated by changing the side groups? Can an exponential decrease in thermal conductance with increasing chain length be realized in custom-designed, disordered polymer chains?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.