Study of Thermal Transport in Single Oligomer and Polymer Chains

该研究项目的主要目标是实验研究热量如何通过单分子链传输。与块状材料相比，研究人员只能对通过单个分子的流动热进行理论计算，其中包括令人惊讶的预测，即热流阻力与分子的长度无关。由于缺乏适当的仪器技术来稳定地保持或限制单分子并以足够的分辨率记录微小的热流，因此单分子热流的直接实验测量仍然是不可能的。在这项提案中，最近在皮瓦分辨率量热法，高分辨率温度测量和实验平台方面取得的突破性实验进展将用于通过系统的实验方法来解决这些具有挑战性的测量。除了技术工作外，该提案还包括广泛的外联活动，以吸引本科生和研究生以及邻近社区中代表性不足的少数民族参与研究。单分子和聚合物链中的热输运，一维系统的优秀近似，是当前的一大兴趣。理论和计算研究，开始与费米，面食和乌拉姆在20世纪50年代，表明傅立叶？的法律一般是无效的一维链，并意味着存在的长度依赖性，发散的热导率。为了验证这些预测，对单个一维链的详细实验测量对于回答以下问题是必不可少的：单个聚合物分子的热导率是什么，它如何依赖于链长，以及热导率是否对所有一维系统发散？单个聚合物分子的热导率可以通过改变侧基来调节吗？在定制设计的无序聚合物链中，随着链长的增加，热导率能否实现指数下降？该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

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.