Interfacial Thermal Resistance Research Articles

A novel carbon-based fiber aerogel with interfacial thermal resistance: Temperature insulation, oxidation resistance, and mechanical performance

A novel carbon-based fiber aerogel with interfacial thermal resistance: Temperature insulation, oxidation resistance, and mechanical performance

Enhanced Thermally Conductive Silicone Grease by Modified Boron Nitride

In this work, a chemical modification method was used to prepare silicone grease with high thermal conductivity. We report two preparation methods for thermal conductive fillers, which are hydroxylated boron nitride-grafted carboxylic silicone oil (h-BN-OH@CS) and amino boron nitride-grafted carboxylic silicone oil (h-BN-NH2@CS). When h-BN-OH@CS and h-BN-NH2@CS were filled with 30 wt% in the base grease, the thermal conductivity was 1.324 W m−1 K−1 and 0.982 W m−1 K−1, which is 6.04 and 4.48 times that of the base grease (0.219 W m−1 K−1), respectively. The interfacial thermal resistance is reduced from 11.699 °C W−1 to 1.889 °C W−1 and 2.514 °C W−1, respectively. Inorganic filler h-BN and organic filler carboxylic silicone oil were chemically grafted to improve the compatibility between h-BN and the base grease. The covalent bond between functionalized h-BN and carboxylic silicone oil is stronger than the van der Waals force, which can reduce the viscosity of the silicone grease.

Cu/oriented-carbon nanotubes composite with ultralow thermal contact resistance

In this paper, a simple material preparation method is proposed to meet the requirements of efficient heat exchange interface materials for spacecraft on-orbit modular assembly. First, carbon nanotubes (CNTs) were uniformly dispersed on the surface of spherical copper (Cu) powder, and then the bulk was obtained by hot-pressing sintering. Finally, the Cu on the surface was removed by electrolysis, so that the CNTs can protrude from the surface to a certain height. After contacting with the matching materials, the exposed CNTs can fill the inevitable pores at the interface, increase the heat transfer channel, and effectively reduce the interface thermal contact resistance (TCR). By adjusting the type of CNT, contact pressure, the height of CNT protruding from the surface of Cu powder, the minimum TCR of the interface between the obtained Cu/oriented carbon nanotube (Cu/OCNT) composite and pure Cu was 25.4 mm2 K W−1 under 2.26 MPa, which is superior to most existing commercial thermal interface materials. Moreover, the heat exchange interface designed based on the prepared materials can be repeatedly contacted and separated, which is expected to provide a solution for the heat exchange of on-orbit modular assembly spacecraft.

Comprehensive analysis of the contribution from the heat capacity in thermal measurement on nanoscale thin films

Nanofilms (NFs) have been widely used in many emerging applications, such as microelectronic devices, spintronics, and optical instruments. Characterizing the thermal conductivity (k) of NFs, kNFs, is nontrivial for both fundamental science and industrial applications. Time-domain thermoreflectance (TDTR) is a powerful technique for thermal characterizations under nano-to-micro-scales. However, both the kNFs and the interface thermal resistance between layers are generally unknown parameters when analyzing TDTR signals. So that an effective thermal resistance model (ETRM) is often utilized, where the impact of heat capacity of NFs, cNFs, has been always ignored. Previous studies have proposed viewpoints on how to validate this assumption, however, which still needs to be verified further by considering the parameters' sensitivities for TDTR signals. In this work, we have highlighted the significance of sensitivity analysis for the investigation of the impact of cNFs with the example experiments on Ni NFs. The error of ETRM has been quantitatively and systematically studied. We found that the application requirements of ETRM in TDTR data analysis rely on the sensitivity relations between kNFs and interface thermal resistance. Finally, suggestions for future characterization of the kNFs have been discussed for reference. Our results and conclusions deepen the understanding of both the transient thermal transport process of multilayer NFs and the ability of TDTR on characterizing kNFs.

A molecular dynamics study of thermal conductivity and viscosity in colloidal suspensions: From well-dispersed nanoparticles to nanoparticle aggregates

This study investigates the microscopic transport behavior of nanofluids addressing some debatable points including the anomalous thermal conductivity (κ), against the predictions of classical effective medium theories. International Nanofluid Property Benchmark Exercise (INPBE) [J. Buongiorno et al., J. Appl. Phys. 106 (2009) 094312] has shown that no such anomaly found in well-dispersed nanofluids after conducting experiments for range of different types of nanofluids. However, a number of molecular dynamics based studies reported otherwise making inconsistent conclusion with INPBE. In this work, it is argued that the over predicted κ values reported in previous computational studies can be attributed to the ill-defined partial enthalpy formulation of the Green-Kubo method for multicomponent systems. Present study begins by addressing this issue via non-equilibrium molecular dynamics and shows that the results are in agreement with the conclusions of INPBE. Further, it is shown that the contribution of potential micro-mechanisms such as micro-convection due to Brownian motion, and the solid-like liquid layering are either absent or suppressed by the interface thermal resistance. The observed decreasing trend of viscosity enhancement to thermal conductivity enhancement ratio (Cη/Cκ) with increasing particle size indicates the improved heat transfer performance in nanofluids with larger nanoparticles. The effect of nanoparticle aggregation, the proposed originative mechanism of anomalous κ, is evaluated arranging nanoparticles as chain-like structures. A 67% improvement in κ is achieved with negligible viscosity variation. This rapidly reduces Cη/Cκ indicating better heat transfer performance with the presence of conductive paths due to the aggregation or in general extended nanostructures.

Interfacial thermal resistance calculations for weak solid–liquid atom interactions using equilibrium molecular dynamics

ABSTRACT This study investigates the use of equilibrium molecular dynamics (EMD) simulations for determining interfacial thermal resistance (ITR) at solid-liquid interfaces. The Green-Kubo theorem is typically used for this purpose, but it may not be suitable for hydrophobic conditions where the interaction between liquid and solid atoms is weak. Two EMD simulation methods were used to calculate ITR at interfaces under different wetting conditions: one using instantaneous temperature differences and the other using instantaneous heat flux. The data derived from the EMD simulation using instantaneous temperature difference could not converge due to weak intermolecular interactions, leading to inaccurate ITR calculations. To address this issue, a method for calculating ITR in the frequency domain is proposed. Results showed that both EMD methods produced different results from non-equilibrium molecular dynamics (NEMD), with the ITR of EMD using instantaneous heat flux being higher than that of NEMD, while the ITR of EMD using instantaneous temperature was lower, and in good agreement with NEMD. Overall, this study highlights the limitations of using EMD simulations for calculating ITR at solid-liquid interfaces in hydrophobic conditions and proposes a new method for improving accuracy in these situations.

The effects of interfacial thermal contact resistance between yarns and matrixes on the thermophysical property of the plain woven C/SiC composite

The plain woven C/SiC composites with high thermal shock resistance are widely used in aerospace applications. For this composite, thermal contact resistance (TCR) has an unneglectable contribution to the thermophysical property. In this work, the influence of the TCR on the thermophysical property of a real 2D plain woven C/SiC composite is studied. X-ray CT scanning is used to obtain the microstructures of the C/SiC composite, and the complex structures are restructured and transformed into standard cube grids based on the theory of the intersection of rays and triangles. Combining with finite difference method (FDM) and multiple GPUs acceleration, an efficient approach for numerically predicting the thermophysical property of the real C/SiC composite is established. Based on the Laser Flash Method (LFM) and Differential Scanning Calorimeter (DSC) method, the effective thermal conductivities (ETCs) of the C/SiC composite at different temperatures are obtained experimentally. The results show that ETCs predicted by our numerical method are closer to the measured ones when TCR is considered. Through the numerical simulation and theoretical analysis, the correlation between the ETC and TCR is obtained, which is proved to be a typical Logistic function, and the physical meanings of various constants in the correlation are determined and discussed. Besides, the thermal response time increases with the TCR increasing, simultaneously, the distributions of isotherms and heat-flux trajectories more approach the distributions of fiber yarns in the material.

Synergistically Improving the Thermal Conductivity and Mechanical Strength of PEEK/MWCNT Nanocomposites by Functionalizing the Matrix with Fluorene Groups

AbstractNanofiller reinforcement is an effective method to prepare high thermally conductive polymer‐matrix composites. However, the poor dispersion of nanofillers and high interfacial thermal resistance between the filler and matrix seriously affect the thermal conductivity and mechanical properties of composites. To solve this problem, a small amount of conjugated fluorene group is introduced into the polymer chain of poly (ether ether ketone) (PEEK) to afford the fluorene‐functionalized copolymer matrix (FD‐PEEK). In an in situ polymerization procedure, the matrix non‐covalently binds to multi‐walled carbon nanotubes (MWCNT) to allow highly filled PEEK/MWCNT nanocomposites. With the filler dispersion and matrix–filler interfacial bonding improved, the prepared nanocomposites possess both high thermal conductivity and tensile strength. At the optimal ratio of 2 mol% fluorene groups in the polymer chain, the nanocomposite with 10 wt% MWCNT exhibits an excellent thermal conductivity of 2.41 W m−1 K−1, which is 868% higher than pristine PEEK, with tensile strength remaining 104.3 MPa. The PEEK/MWCNT nanocomposites can be further used as matrix resins to build double‐segregated network multi‐component composites, which contributes to an innovative strategy to design high‐performance thermally conductive materials.

Effects of Structure Defects on Thermal Transport at the Graphene–Water Interface

AbstractThe graphene microchannel heat sinks have attracted extensive attention due to its high cooling efficiency in microelectric devices. The interfacial thermal resistance (ITR) between graphene as the bottom layer of microchannel and water is one of the key factors of its good working performance. In this paper, the impacts of structure defects in graphene surfaces on ITR of the graphene–water interface are investigated using molecular dynamic simulations. The results indicate that graphene layer with different types of structure defects shows different variation trends of ITR as the defect concentration or temperature increases. A peak ITR reduction of nearly 30% is generated with the Stone‐Wales defect of 2%. Finally, the density of phonon states and interfacial binding energy analysis are performed to verify the correctness of the simulation results. The present work expands the understanding of structure defects effect on thermal transport in graphene microchannel.

Covalently interconnected carbon nanotubes network enhancing thermal conductivity of EP-based composite

The miniaturization of integrated circuits promotes the rapid rise of polymer-based carbon nanotubes (CNTs) thermal conductive composites. However, the unordered arrangement structure and interfacial thermal resistance of CNTs become important obstacles affecting their application. The directional orientation driven of CNTs by external force and the “bridge” between CNTs constructed via covalent bonding could solve these issues. Herein, the freeze-casting orientation configuration and new CNTs grew in situ by ZIF-67 constructed the hierarchical structure of CNTs in epoxy resin (EP)-based composites. The composites with directional networks of interlinked CNTs achieve an out-plane thermal conductivity value (κ⊥) of 0.98 W m−1 K−1 at filler loading of 5.8 vol%, which is 4.85 times high than that of pure EP. More importantly, non-equilibrium molecular dynamics (NEMD) simulations validated the advantage of using covalent bonding to connect CNTs. This work provides a way for the reasonable design of polymer-based CNTs thermal conductive composites.

Microwave absorption and thermal conductivity properties in NPC@MoSe2/PDMS composites

As electronic devices develop rapidly toward miniaturization and integration, electromagnetic wave (EMW) interference and heat accumulation problems have risen sharply, thus thermal conductivity-EMW absorption integrated materials (HCMAMs) have received extensive attention. Herein, a dual-function hierarchical porous NPC@MoSe2 filler was constructed by salt-template-assisted freeze-drying, calcination and hydrothermal reaction. 3D Nitrogen-doped porous carbon (NPC), a thermal and conductive path, is the prerequisite for the integration of EMW absorption and thermal conduction. Dense MoSe2 layer reduces the discrepancy of impedance and phonon frequency between NPC and Polydimethylsiloxane (PDMS), optimizing the impedance matching and reducing the interface thermal resistance. Remarkably, under the fillings of only 15 w%, NPC@MoSe2-2/PDMS exhibits optimal EMW absorption with a minimum reflection loss (RLmin) of −51.6 dB@18 GHz and an effective bandwidth (EAB) of 7.1 GHz, and excellent thermal conductivity performance with a thermal conductivity of 0.97 W/m·K, which is 304% higher than that of pure PDMS. Overall, this dual-functional NPC@MoSe2-2/PDMS has great potential in protecting integrated electronic devices.

Optimization of interfacial mixing for thermal transport along Si/Ge heterostructures: A molecular dynamics study

Interfaces can play critical roles in the dissipation of heat, generated during the electronic nanodevices operation. Therefore, engineering of the interfacial thermal resistance is a key factor in the thermal management design of nanoelectronics. In this research, the engineering of the interfacial thermal resistance of silicon/germanium heterostructure is explored, by varying the content of silicon or germanium atoms at the interphase (mixing region). For this goal, we conducted systematic non-equilibrium molecular dynamics simulations. For a specific interphase length, it is noticeably predicted that the interfacial thermal resistance versus the percentage of germanium atoms shows an optimal minimum value. By substituting germanium atoms with silicon atoms, but with preserving their atomic mass, it is interestingly shown that the interfacial thermal resistance increases significantly, although the optimal value for the interfacial thermal resistance is still observable. By altering the length of the interphase region and the samples’ temperature (300 and 600 K), the optimal interfacial thermal conductance in terms of the percentage of germanium atoms in the mixing region was also detectable. The findings of this work can be useful in the thermal management engineering of nanodevices, especially in nanoelectronics.

Investigations on Thermal Conductivity of Two-Phase WC-Co-Ni Cemented Carbides through a Novel Model and Key Experiments

Excellent thermal conductivity is beneficial for the fast heat release during service of cemented carbides. Thus, thermal conductivity is a significant property of cemented carbides, considerably affecting their service life. Still, there is a lack of systematic investigation into the thermal conductivity of two-phase WC-Co-Ni cemented carbides. To remedy this situation, we integrated experiments and models to study its thermal conductivity varying the phase composition, temperature and WC grain size. To conduct the experiments, WC-Co-Ni samples with two-phase structure were designed via the CALPHAD (Calculation of Phase Diagrams) approach and then prepared via the liquid-phase sintering process. Key thermal conductivity measurements of these prepared samples were then taken via LFA (Laser Flash Analysis). As for modeling, the thermal conductivities of (Co, Ni) binder phase and WC hard phase were firstly evaluated through our previously developed models for single-phase solid solutions. Integrating the present key measurements and models, the values of ITR (Interface Thermal Resistance) between WC hard phase and (Co, Ni) binder phase were evaluated and thus the model to calculate thermal conductivity of two-phase WC-Co-Ni was established. Meanwhile, this model was verified to be reliable through comparing the model-evaluated thermal conductivities with the experimental data. Furthermore, using this developed model, the thermal conductivity of two-phase WC-Co-Ni varying with phase-fraction, temperature and grain size of WC was predicted, which can contribute to its design for obtaining desired thermal conductivities.

Thermal resistance from non-equilibrium phonons at Si–Ge interface

As nanostructured devices become prevalent, interfaces often play an important role in thermal transport phenomena. However, interfacial thermal transport remains poorly understood due to complex physics across a wide range of length scales from atomistic to microscale. Past studies on interfacial thermal resistance have focused on interface-phonon scattering at the atomistic scale but overlooked the complex interplay of phonon-interface and phonon-phonon scattering at microscale. Here, we use the Peierls-Boltzmann transport equation to show that the resistance from the phonon-phonon scattering of non-equilibrium phonons near a Si–Ge interface is much larger than that directly caused by the interface scattering. We report that non-equilibrium in phonon distribution leads to significant entropy generation and thermal resistance upon three-phonon scattering by the Boltzmann's H-theorem. The physical origin of non-equilibrium phonons in Ge is explained with the mismatches of phonon dispersion, density-of-states, and group velocity, which serve as general guidance for estimating the non-equilibrium effect on interfacial thermal resistance. Our study bridges a gap between atomistic scale and less studied microscale phenomena, providing comprehensive understanding of overall interfacial thermal transport and the significant role of phonon-phonon scattering.

Laser Thermal Wave Diagnostics of the Thermal Resistance of Soldered and Bonded Joints in Semiconductor Structures.

This paper is a review of recent applications of a laser photothermal mirage technique for sensing and measuring the thermal resistance of joint layers in modern electronic devices. A straightforward theoretical model of the interfacial thermal resistance based on the formation of a thin intermediate layer between jointed solids is described. It was experimentally shown that thermal properties of solder layers cannot be evaluated simply on the base of averaging the thermal properties of solder components. The review presents the laser thermal wave methodology for measuring thermal parameters of soldered and adhesively bonded joints. The developed theoretical model makes it possible to carry out a quantitative estimation of local thermal conductivities of joints and their thermal resistances by fitting theoretical results with experimental data obtained by the laser beam deflection method. The joints made with lead-containing and lead-free solders were studied. The anomalous distribution of thermal properties in the solder layer is explained by the diffusion of various atoms detected by energy dispersive X-ray spectroscopy. The laser beam deflection method made it possible to reveal a strong influence of the surface pretreatment quality on the interfacial thermal resistance.

Lightweight All Graphene‐Based Two‐Phase Heat Transport Devices

AbstractGraphene‐based composites show great potential in the development of lightweight functional devices and systems, and polymers are usually used as binders to enhance the mechanical properties of these composites. Due to the low thermal conductivity of the polymer and the high inherent interfacial thermal resistance between polymer and graphene, however, the developed devices and systems generally possess low thermal conductivity, which seriously limits their further thermal‐related applications. Here, a lightweight two‐phase heat transport device (TPHTD) based on a vapor‐liquid phase transition‐based heat transfer by using a graphene‐based composite material as the casing is generated. The graphene‐based TPHTD has high thermal conductivity of up to 1408 W (mK)−1 and realizes ultra‐high specific thermal conductivity of ≈5600 W (mKg)−1. This graphene‐based device with lightweight and high heat transfer capacity offers new opportunities for efficient thermal management of compact, portable, or wearable electronic and power systems.

Thermal conductivity in metallic nanoparticle-packed beds

Understanding heat transport properties of metallic nanoparticle-packed beds (NPBs) is important for further tuning their thermal conductivities. In this work, we aim to understand the thermal contact resistance between nanoparticles through establishing a theoretical model comprising background thermal resistance (Rbulk), thermal contact resistances between particles (Rcontact), and interfacial thermal resistance between solid and air (Rinter). To valid the theoretical model, copper NPBs were firstly prepared by applying cold-pressing method, and then the thermal conductivity (TC) was measured by utilizing hot-wire method. Results show that our model could match the experiment well. TC of copper NPBs is ultra-low compared with that of bulk Copper. This extremely low TC of Copper NPBs is attributed to the large Rcontact generated at the interface by electron boundary scattering. This study is expected to supply some information for tuning TC of metallic nanoparticles packed beds.

Enhancing thermal transport across diamond/graphene heterostructure interface

The thermal properties of two-dimensional materials and their heterostructure are critical for efficient heat dissipation in nano-devices. A good example is graphene which exhibits excellent in-plane thermal transport properties. However, the substantial interfacial thermal resistance between graphene and the substrate greatly hinders its practical application. Diamond is a good choice as a substrate to reduce out-of-plane phonon scattering when graphene is contacted with the substrate because of their high structural similarity. Based on non-equilibrium molecular dynamics simulations, the effects of graphene layer count and the temperature on the thermal conductance of diamond/graphene heterostructure are investigated. The results show that the interfacial thermal conductance of diamond/single-layer graphene heterostructure is at least double that of diamond/multi-layer graphene heterostructure. Moreover, high temperature is also conducive to thermal transport for diamond/graphene heterostructure. Due to the anisotropy of graphene, the in-plane and out-of-plane phonon density of state were analyzed. The trend of overlap energy of out-of-plane phonon density of state is consistent with that of the interfacial thermal conductance, which suggests that out-of-plane phonon has a greater effect on heat transport at the interface. The increasing temperature excites more high-frequency phonons, and thus, promotes the phonon coupling of diamond and graphene. This well explains the increases in interfacial thermal conductance at a higher temperature.

Graphene/carbon fiber network constructed by co-carbonization strategy for functional integrated polyimide composites with enhanced electromagnetic shielding and thermal conductive properties

With the rapid development of electronic information and technology, materials with electromagnetic interference (EMI) shielding and thermal management are playing an increasingly important role in the semiconductor industry. However, the strategy of synthesizing the above dual-functional materials remain a challenge. Herein, the interconnected graphene/carbon fiber networks constructed by a facile co-carbonation strategy was reported to obtain the polyimide composites with EMI shielding properties and thermal conductivity (TC). The composite exhibited superior EMI shielding of ∼ 73 dB at the thickness of 2 mm when the carbon network content is 20 wt%. Moreover, the through-plane TC of the composite reaches 1.65 W·m−1·K−1, which is 611% higher than that of polymer matrix. We attribute the increased EMI shielding and TC properties to the construction of graphene/carbon fiber co-carbonation network, which provides an efficient and continuous electric conductive and thermally conductive network in the polyimide matrix. Moreover, the co-carbonation network can increase the polarization loss of electromagnetic waves while decreasing the interfacial thermal resistance between fillers. The structural–functional integration strategy is helpful for developing new high-performance dual-functional composites for the electronics and aerospace industries.

Using Thermal Interface Resistance for Noninvasive Operando Mapping of Buried Interfacial Lithium Morphology in Solid-State Batteries.

The lithium metal-solid-state electrolyte interface plays a critical role in the performance of solid-state batteries. However, operando characterization of the buried interface morphology in solid-state cells is particularly difficult because of the lack of direct optical access. Destructive techniques that require isolating the interface inadvertently modify the interface and cannot be used for operando monitoring. In this work, we introduce the concept of thermal wave sensing using modified 3ω sensors that are attached to the outside of the lithium metal-solid-state cells to noninvasively probe the morphology of the lithium metal-electrolyte interface. We show that the thermal interface resistance measured by the 3ω sensors relates directly to the physical morphology of the interface and demonstrates that 3ω thermal wave sensing can be used for noninvasive operando monitoring the morphology evolution of the lithium metal-solid-state electrolyte interface.