Thermal Transport through Individual Surface Modified Carbon Nanotubes and Their Contacts Carbon nanotubes (CNTs), because of their superior mechanical, electrical and thermal properties, have been extensively tested as nanostructure additives to tune the properties of CNT-polymer composites. While the measured electrical conductivity of CNT-polymer composites can be seven orders of magnitude higher than that of pure polymers, the increase in thermal conductivity is mild and far from the prediction based on the classical particle mixing theory. This apparent dissimilarity attracted significant attention and studies. However, to date, a thorough understanding is still missing.
The objective of the proposed research program is to understand, through systematic measurements at individual nanostructure level, thermal transport through individual CNTs, contacts between individual CNTs, and interfaces between CNTs and polymer molecules. The measurements will be performed with both non-modified CNTs and surface modified CNTs attached with polymer molecules via either non-covalent or covalent bonds.
The proposed study is different from the traditional mix and measure approach, in which CNTs and polymers are first mixed and cured into solid composites and then the thermal conductivity of resulted materials is measured. The mix and measure approach leads to inconsistent results and more importantly, thermal transport through nanostructures and their contacts has to be inferred from the measured results of bulk samples with many assumptions of the composite structure and morphology. Therefore, it is difficult to draw solid conclusions. The proposed experimental studies, on the contrary, will directly measure thermal transport through individual nanostructures and their contacts, together with careful characterization of the measured samples structure and morphology. We believe that the proposed systematic study will lead to solid experimental data, which will answer the following fundamental questions: (1) How do energy carriers transport through CNT-CNT contacts and how does the contact conductance scale with the contact area (2) How does thermal energy transport through the interfaces between CNTs (hard) and polymer (soft) materials (3) How do polymer molecules affect energy transport through CNT-CNT contacts Based on the obtained fundamental understanding, we can create new design rules for using CNTs to tune the transport properties of CNT-polymer composites.
The intellectual merit of the project resides in the previously unavailable experimental data of thermal transport through surface modified CNTs, CNT-CNT contacts and CNT-polymer interfaces. More importantly, these data will lead to new or deeper physical understanding of nanoscale thermal transport that can answer many fundamental scientific questions about energy transport through various nanostructures involving CNTs, their contacts and CNT-polymer hybrids. The proposed systematic studies will be especially helpful to discover the dependence of thermal transport through CNTs and their contacts as a function of the CNT diameter, which will disclose intriguing nanoconfinement effects on energy transport.
The broader impacts include new design rules based on the obtained insights of nanoscale transport phenomena, which could be used to tune the transport properties of CNT-polymer composites. This will lead to technology advancement of high-performance CNT-polymer hybrid materials important for extensive applications such as flexible microelectronics and thermoelectric/photovoltaic energy conversion. In addition, the proposed integrated research and education plan will educate graduate students in an interdisciplinary environment and the research results will be widely disseminated through scientific publications and classroom instructions. The research impacts will also be extended to undergraduate, underrepresented, and K-12 students through leveraging Vanderbilt's various education and outreach programs.