Session: Rising Stars of Mechanical Engineering Celebration & Showcase

Paper Number: 149689

149689 - Pushing the Lower Limit of Thermal Conductivity in Layered Materials 

Identifying effective strategies to achieve exceptionally-low thermal conductivity in solid-state materials aligns with the long-term goal in thermal transport community to push the extremes in heat conduction. The success of this project will ultimately lead to transformative opportunities to realize novel thermal-control functionalities in disordered layered materials, such as directional-heat-spreading and thermal-switching. Moreover, fundamental understanding of thermal transport processes in disordered materials has translational implications in sustainable energy infrastructure, such as energy savings by thermal insulation, energy storage in batteries, energy conversion in thermoelectrics, and thermal management in electronics. The integration of research, education, and outreach programs aims to raise the public awareness of challenges in sustainable energy, and motivate students to pursue appropriate education pathways to STEM occupations. Cinematic 360 Virtual Reality lab tours will be developed to ‘teleport’ online K-12 students into the lab to visualize thermal transport research and applications in sustainable energy. Teachers will be invited to collaborate and pilot educational activities promoting the importance and challenges in sustainable energy infrastructure. The enhancement of students' preparation for a STEM career will be achieved by a summer program with a particular emphasis on reaching out to female and/or African-American students.

The research goal is to understand how to suppress vibrational energy transport in anisotropic layered materials by disorder. Precise and reversible control of the degree and inhomogeneity of disorder and thus interlayer spacing is achieved by an electrochemistry or spin-coating process, which inserts ions or molecular chains into the van der Waals gaps of layered crystals. The investigations will focus on a model layered crystal, using complementary state-of-the-art theoretical and experimental approaches. First, thermal conductivity of bulk crystals with a controllable amount and type of ions or molecular chains inserted into the gaps will be measured by the time-domain thermoreflectance method. Then, the contribution from different types of vibrational modes to the microscopic thermal transport in these disordered crystals will be analyzed using a combination of lattice dynamics and molecular dynamics methods. The success of this project will enable the first set of experimental and theoretical studies to elucidate the roles of interlayer spacing and bonding environment on suppressing vibrational energy transport, advancing the current understanding on the microscopic thermal transport mechanisms in anisotropic disordered layered materials.

We have successfully found a class of materials, hybrid organic-inorganic layered metal halide perovskite, with exceptionally low thermal conductivity while the elastic modulus stays high. Via molecular engineering, we can tune the organic-organic interface in these materials, thus precisely controlling their thermal conductivity. We will continue to push the extremes of heat conduction in fully dense solids.

Presenting Author: Jun Liu North Carolina State University

Presenting Author Biography: Dr. Jun Liu is currently an Associate Professor in the Department of Mechanical and Aerospace Engineering at North Carolina State University. Prior to this, he was a postdoctoral research associate in the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. He received his Ph.D. in Mechanical Engineering from University of Colorado at Boulder in December 2013. He earned his B.S. in 2008 from Power and Energy Engineering at Huazhong University of Science and Technology. He is the recipient of the NC State University Outstanding Teacher Award in 2023, NSF CAREER Award in 2020, and Outstanding Dissertation Award in 2013.

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