Interfacial Thermal Conductivity and Its Anisotropy

There is a significant effort in miniaturizing nanodevices, such as semi-conductors, currently underway. However, a major challenge that is a significant bottleneck is dissipating heat generated in these energy-intensive nanodevices. In addition to being a serious operational concern (high temperatures can interfere with their efficient operation), it is a serious safety concern, as has been documented in recent reports of explosions resulting from many such overheated devices. A significant barrier to heat dissipation is the interfacial films present in these nanodevices. These interfacial films generally are not an issue in macro-devices. The research presented in this paper was an attempt to understand these interfacial resistances at the molecular level, and present possibilities for enhancing the heat dissipation rates in interfaces. We demonstrated that the thermal resistances of these interfaces were strongly anisotropic; i.e., the resistance parallel to the interface was significantly smaller than the resistance perpendicular to the interface. While the latter is well-known—usually referred to as Kapitza resistance—the anisotropy and the parallel component have previously been investigated only for solid-solid interfaces. We used molecular dynamics simulations to investigate the density profiles at the interface as a function of temperature and temperature gradient, to reveal the underlying physics of the anisotropy of thermal conductivity at solid-liquid, liquid-liquid, and solid-solid interfaces.

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Thermal Transport in Self-Assembled Conductive Networks for Thermal Interface Materials

Journal of Electronic Packaging ◽

10.1115/1.4003865 ◽

2011 ◽

Vol 133 (2) ◽

Author(s):

Lin Hu ◽

William Evans ◽

Pawel Keblinski

Keyword(s):

Thermal Conductivity ◽

Effective Thermal Conductivity ◽

Volume Fraction ◽

Liquid Solution ◽

Thermal Interface Materials ◽

Thermal Interface ◽

Rapid Formation ◽

Dynamics Simulations ◽

Solid Liquid ◽

Interface Materials

We present a concept for development of high thermal conductivity thermal interface materials (TIMs) via a rapid formation of conductive network. In particular we use molecular dynamics simulations to demonstrate the possibility of a formation of a network of solid nanoparticles in liquid solution and establish wetting and volume fraction conditions required for a rapid formation of such network. Then, we use Monte-Carlo simulations to determine effective thermal conductivity of the solid/liquid composite material. The presence of a percolating network dramatically increases the effective thermal conductivity, as compared to values characterizing dispersed particle structures.

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Thermal Conductivity and Thermal Mechanism of Octadecane from Molecular Dynamics Simulations

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.501.139 ◽

2012 ◽

Vol 501 ◽

pp. 139-144

Author(s):

Qing Ling Li ◽

Wen Juan Zheng ◽

Yan Wang ◽

Yan Zhou

Keyword(s):

Heat Transfer ◽

Phase Transition ◽

Thermal Conductivity ◽

Contact Interface ◽

Transfer Resistance ◽

Material Studio ◽

Increasing Trend ◽

Thermal Mechanism ◽

Dynamics Simulations ◽

Solid Liquid

The physical model of the octadecane in the paraffin is established by Material Studio software in this paper, thermal conductivity and micro-thermal mechanism of octadecane are simulated by program LAMMPS. Results show that: the thermal conductivity of octadecane is about , which has an increasing trend with enhancement of temperature; simultaneously it mainly relies on the molecular or atomic thermal vibration to transmit heat. When the octadecane has phase transition, reducing of thermal conductivity is due to the increasing of heat transfer resistance of solid-liquid contact interface.

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Thermal Conduction Behaviors of PAAm Hydrogels

10.20944/preprints201710.0162.v1 ◽

2017 ◽

Author(s):

Ni Tang ◽

Zhan Peng ◽

Rulei Guo ◽

Meng An ◽

Xiandong Chen ◽

...

Keyword(s):

Thermal Conductivity ◽

Water Content ◽

Thermal Conduction ◽

Heat Dissipation ◽

Phonon Scattering ◽

Soft Materials ◽

Crosslinking Density ◽

Critical Issue ◽

New Class ◽

Dynamics Simulations

As the interface between human and machine becomes blurred, hydrogel incorporated electronics and devices have emerged to be a new class of flexible/stretchable electronic and ionic devices due to their extraordinary properties, such as soft, mechanically robust and biocompatible. However, heat dissipation in these devices could be a critical issue and remains unexplored. Here, we report the experimental measurements and equilibrium molecular dynamics simulations of thermal conduction in polyacrylamide (PAAm) hydrogels. The thermal conductivity of PAAm hydrogels can be modulated by both the crosslinking density and water content in hydrogels. The crosslinking density dependent thermal conductivity in hydrogels varies from 0.33 to 0.51 Wm-1K-1, giving a 54% enhancement. We attribute the crosslinking effect to the competition between the increased conduction pathways and the enhanced phonon scattering effect. Moreover，water content can act as filler in polymers which lead to nearly 40% enhancement in thermal conductivity in PAAm hydrogels with water content vary from 23 to 88 wt%. Furthermore，we find the thermal conductivity of PAAm hydrogel is insensitive to temperature in the range of 25 oC – 40 oC. Our study offers fundamental understanding of thermal transport in soft materials and provides design guidance for hydrogel-based devices. 

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Numerical Study of the Effective Thermal Conductivity of Nanofluids

Heat Transfer: Volume 1 ◽

10.1115/ht2005-72577 ◽

2005 ◽

Cited By ~ 5

Author(s):

Ratnesh K. Shukla ◽

Vijay K. Dhir

Keyword(s):

Thermal Conductivity ◽

Numerical Study ◽

Free Particle ◽

Liquid System ◽

Bulk Liquid ◽

Dynamics Simulations ◽

Solid Liquid ◽

Base Liquid ◽

Liquid Layering ◽

Ordered Layers

Nanofluids, that is liquids containing nanometer sized metallic or non-metallic solid nanoparticles show an increase in thermal conductivity compared to that of the base liquid. In this paper we present numerical results obtained from Molecular Dynamics Simulations of a solid-liquid system comprising of Lennard-Jones atoms used to study the liquid layering on solid nanoparticles. It is found that close to the solid surface the liquid atoms form ordered layers which display higher thermal conductivity compared to the bulk liquid. We also present a model for thermal conductivity of nanofluids based on the theory of Brownian motion of a free particle and show that the thermal conductivity of the nanofluid predicted from the model agrees qualitatively with the experimental observations.

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Vibrational Contribution to Thermal Conductivity of Silicon Near Solid-Liquid Transition

Volume 10: Heat and Mass Transport Processes, Parts A and B ◽

10.1115/imece2011-64064 ◽

2011 ◽

Author(s):

Christopher H. Baker ◽

Chengping Wu ◽

Richard N. Salaway ◽

Leonid V. Zhigilei ◽

Pamela M. Norris

Keyword(s):

Thermal Conductivity ◽

Molecular Dynamics ◽

Melting Point ◽

Silicon Substrates ◽

Liquid Transition ◽

Electron Contribution ◽

Non Equilibrium Molecular Dynamics ◽

Dynamics Simulations ◽

Solid Liquid ◽

Vibrational Contribution

Although thermal transport in silicon is dominated by phonons in the solid state, electrons also participate as the system approaches, and exceeds, its melting point. Thus, the contribution from both phonons and electrons must be considered in any model for the thermal conductivity, k, of silicon near the melting point. In this paper, equilibrium molecular dynamics simulations measure the vibration mediated thermal conductivity in Stillinger-Weber silicon at temperatures ranging from 1400 to 2000 K — encompassing the solid-liquid phase transition. Non-equilibrium molecular dynamics is also employed as a confirmatory study. The electron contribution may then be estimated by comparing these results to experimental measurements of k. The resulting relationship may provide a guide for the modeling of heat transport under conditions realized in high temperature applications, such as laser irradiation or rapid thermal processing of silicon substrates.

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