Penn Engineering


Research Areas


Research Group




Contact Us


Emergent Behavior of Thermally Coupled Nanostructures

(Funding: Office of Naval Research , National Science Foundation CAREER Award )

A primary research focus of our group is the emergent thermal transport behavior of nanostructures configured in complex arrays, systems spanning multiple length scales, and nanocomposite materials. A key goal of this research is to develop experimentally validated simulation methodologies to couple disparate length scales. Work in this area includes the following projects:

Nanocomposites for Improved Thermal Conductivity

In this project, we have investigated the thermal conductivity of polymer-carbon nanotube composite materials with an aim toward developing better materials for enhanced heat removal from high temperature electronics. Our results indicate that thermal conduction in the composites occurs through percolation, and suggest the intriguing possibility that thermal resistances in the system are dramatically reduced by polyethylene crystallites that nucleate at carbon nanotube surfaces and bridge adjacent nanotubes.

Interfacial Thermal Resistance between Carbon Nanotubes

We have investigated the length, spacing, and overlap dependence of thermal interfacial resistance between carbon nanotubes. Interestingly, our studies have found that thermal tunneling between the nanotubes across a vacuum gap can occur even at large spacings due to intermittent thermal fluctuations that drive atoms in neighboring nanotubes toward each other.

Superlattice Thermal Transport

We have investigated the thermal transport characteristics of superlattices and superlattice nanowires. The major accomplishment of this research was the identification of interfacial strain as a key factor influencing thermal transport. For example, we found that interfacial strain causes superlattice minimum conductivity to vanish. Also, we found that thermal resistance at individual interfaces in superlattice nanowires increased with increasing superlattice period due to pronounced strain variation across the interfacial region.

Modulated Thermoreflectance Thermal Transport Measurements

We have established a modulated thermoreflectance laser setup for thermal conductivity measurements of nanostructured (and other) materials. In the experiment, a modulated laser beam is used to heat the sample, and a second, continuous laser beam is used to probe the resultant reflectivity variation. The amplitude and phase of the measured reflectivity signal are used, in conjunction with an analytical model, to determine thermal conductivity. Additionally, the setup has a scanning capability for nondestructive structural evaluation.

Relevant Publications
R. Haggenmueller, C. Guthy, J. R. Lukes, J. E. Fischer, and K. I. Winey, 2007, Single Wall Carbon Nanotube/Polyethylene Nanocomposites. Thermal and Electrical Conductivity, Macromolecules, Vol. 40, pp. 2417-2421.
H. Zhong and J. R. Lukes, 2006, Interfacial Thermal Resistance between Carbon Nanotubes: Molecular Dynamics Simulations and Analytical Thermal Modeling, Physical Review B, Vol. 74, 125403. (Selected for the September 18, 2006 issue of Virtual Journal of Nanoscale Science and Technology)
Y. Chen, D. Li, J. R. Lukes, Z. Ni, and M. Chen, 2005, Minimum Superlattice Thermal Conductivity from Molecular Dynamics, Physical Review B, Vol. 72, 174302. (Selected for the November 21, 2005 issue of Virtual Journal of Nanoscale Science and Technology)
Y. Chen, D. Li, J. Yang, Y. Wu, J. R. Lukes, and A. Majumdar, 2004, Molecular Dynamics Study of the Lattice Thermal Conductivity of Kr/Ar Superlattice Nanowires, Physica B, Vol. 349, pp. 270-280.
Y. Chen, D. Li, J. Yang, Z. Ni, and J. R. Lukes, 2004, Interface Effect on Lattice Thermal Conductivities of Superlattice Nanowires, Proceedings of the 2004 International Mechanical Engineering Congress and Exposition, November 13-20, 2004, Anaheim, California, IMECE2004-59149.

© Nanoscale Engineering Laboratory Lukes Research Group