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The Myth of Interfacial Thermal Resistance: Why is there still resistance to heat flow between perfect materials?
In modern materials science, interface thermal resistance, also known as thermal boundary resistance or Kapitza resistance, is an important concept used to quantify the resistance to heat flow between two materials. Although the terms are used interchangeably, Kapitza resistance generally refers to an atomically perfect, flat interface, while thermal boundary resistance is a broader term. This thermal resistance is different from contact resistance because it still exists even in an atomically perfect interface.
When energy carriers (such as phonons or electrons) attempt to cross an interface, scattering occurs at the interface due to differences in the electronic and vibrational properties of different materials.
This interface thermal resistance will result in a finite temperature discontinuity at the interface when a constant heat flux is applied to the interface. Many theoretical models have been proposed to describe this phenomenon, including the phonon gas model and the acoustic mismatch model (AMM) and the diffusion mismatch model (DMM), which play an important role in how to predict the mechanism of heat flow.
In nanoscale systems, the impact of interface effects is more significant and plays a key role in the thermal properties of materials. When it comes to high thermal dissipation applications such as microelectronic semiconductor devices, low thermal resistance material interfaces are critical to achieve efficient heat dissipation. According to the predictions of the International Technology Roadmap for Semiconductors (ITRS), it faces a heat flux density requirement of up to 100,000 W/cm², which is a huge challenge compared with current technology.
The study of thermal boundary resistance is critical to understanding material interfaces and enhancing their thermal properties.
On the other hand, in applications that require good thermal insulation, such as aircraft engine turbines, material interfaces with high thermal resistance may be required, especially those that are stable at high temperatures. For example, current metal-ceramic composites may be suitable for such applications.
Concerning the impact of interface thermal resistance, there are two main prediction models worthy of attention: the acoustic mismatch model (AMM) and the diffusion mismatch model (DMM). AMM assumes that the interface is perfect and phonons are transferred elastically between the interfaces, while DMM assumes that the interface exhibits diffusive scattering, which is more accurate in high-temperature environments.
Molecular dynamics (MD) simulations have become a powerful tool for studying interfacial thermal resistance and have shown that solid-liquid interfacial thermal resistance can be reduced by strengthening solid-liquid interactions on nanostructured solid surfaces. .
Regarding the limitations of these models, there are significant differences in the way AMM and DMM handle scattering, with AMM assuming a flawless interface and DMM treating it as a fully scattering interface. Therefore, in reality, these models often cannot effectively describe the thermal interface resistance, but can serve as upper and lower bounds for real behavior.
In the theoretical model relative to room temperature, research on liquid helium first proposed the existence of interface thermal resistance. In 1936, the interfacial resistance of liquid helium was being confirmed, but the actual heat conduction behavior was not systematically studied until 1941 by Pyotr Kapitsa. The acoustic mismatch model he proposed could only predict an error of two orders of magnitude at best, so subsequent research work gradually moved towards other heat transfer mechanisms.
In the application of materials science, carbon nanotubes have attracted attention due to their excellent thermal conductivity, and interface thermal resistance is one of the key factors affecting their effective thermal conductivity. This area remains relatively underexplored and has stimulated much research interest.
As the exploration of the basic mechanism deepens, the study of interface thermal resistance will receive more and more attention. How will this knowledge contribute to innovations in thermal management and materials design in the future?
