ISTP-33

Heat Conduction in Liquids, Soft Matters, and over Interfaces:
A Molecular Dynamics View

Professor Taku Ohara

Institute of Fluid Science, Tohoku University,
Sendai, Japan.

Macroscopic heat conduction is composed of molecular-scale thermal energy transfer. The molecular-scale analysis is significant when we consider (1) macroscopic thermophysical properties, (2) nanoscale systems where the material exhibits different nature from macroscopic bulk materials, and (3) interfaces between different materials/phases. As for (1), the thermal conductivity of bulk material is determined by an accumulation of inter- and intramolecular transfer of molecular kinetic energy. The knowledge of the molecular-scale mechanism helps not only tells us how the thermal conductivity of this material exhibits this specific value but also gives way to tuning thermophysical properties of the material by designing molecules with best-fit functional atomic groups. This is useful especially for liquids and soft matters where no insightful theory exists, unlike the phonon transport in crystal solids and molecular gas dynamics for gases. As for (2), the examples are transport phenomena in molecular membranes and nanoscale liquids confined by solid walls. This is somewhat related to (3). The transport phenomena at interfaces are getting important recently because modern advanced nanotechnology produces a wide variety of nanoscale systems whose physical properties are influenced significantly by the characteristics of their interfaces. One of the most urgent tasks in this regard is reducing thermal boundary resistance to achieve better heat transfer. Solid-solid junctions with thermal interface materials (TIM) in between and nanocomposites made of liquids or soft matters with suspensions of nanomaterials are studied extensively. The molecular-scale analysis provides the macroscopic characteristics, i.e., thermophysical properties and interfacial thermal resistance, to the continuum dynamics for further macroscopic analysis. In these three decades, the author and collaborators have been engaged in molecular dynamics (MD) analysis of these kinds. The thermal energy transfer phenomena in the molecular view will be presented here.
(Acknowledgments)
This work is supported by JST CREST JPMJCR17I2 and JSPS Kakenhi 20K04300.

About Professor Taku Ohara

Professor Taku Ohara received B. Eng., M. Eng., and Dr. Eng. in Mechanical Engineering from The University of Tokyo, Japan in 1986, 1988, and 1991, respectively. He joined Tohoku University in 1991 and has been a full professor since 2006. His research interests are Nano- and molecular-scale heat and fluid flow, molecular thermophysical properties, and interfacial thermal phenomena.
Prof. Ohara has received many awards such as:

• Best Paper Awards from JSME (Japan Society of Mechanical Engineers) in 1993 and 2009.
• Young Investigator Award from JSFM (Japan Society of Fluid Mechanics) in 2001.
• Academic Achievement Awards from HTSJ (Heat Transfer Society of Japan) in 2004, 2013 and 2019.
• Best Paper Award from JSTP (Japan Society of Thermophysical Properties) in 2011.
• Academic Achievement Award from Thermal Engineering Division, JSME in 2011.

He is also active in many academic services, including:

• 2020: President of JSTP (Japan Society of Thermophysical Properties)
• 2021: Head of Thermal Engineering Division of JSME
• Currently:
  Executive Board director of JSME
  Executive Board member of AUTSE (Asian Union of Thermal Science and Engineering)
  Scientific Council member of ICHMT (International Centre for Heat and Mass Transfer)
  Editor of International Journal of Heat and Mass Transfer