Search

Highlights Despite the continuous development and improvement of many technologies and multifunctional materials for the electric powertrain (ePowertrain) for electric vehicles, there are still technical issues and challenges to address such as thermal management in batteries, electric motors, and power electronic devices, as most of their failures are due to poor thermal management. Consequently, conventional engineering polymer materials already used must be replaced since most of them have low thermal conductivity and are therefore limited in performance for thermal management applications. A key solution is to develop highly thermally conductive polymer composites that combine other features, such as flame‐retardant, electrical insulation, and mechanical and barrier properties, by incorporating fillers into the polymer matrix. This approach has attracted intensive research efforts. In this review, we first examine the key drivers, trends, and solutions of the ePowertrain segment, emphasizing thermal management. Second, special attention is given to the state‐of‐the‐art boron nitride (BN) polymer composites with current or potential applications in the automotive industry, especially, in batteries, electric motors, and power electronics. Third, analysis and prediction of thermal properties of BN polymer composites by finite element simulation are presented. Finally, outlooks for future research in this field are highlighted. Thermal management of batteries, electric motors and power electronics, using BN polymer composites, optimizes the functionality of electric vehicles. Cross‐linked polymers with BNNSs provide resins for high power motors, film capacitors, and Li‐metal battery electrolytes for electric vehicles. Mathematical modeling and life cycle analysis can predict trends and research gaps in ePowertrain applications. [ABSTRACT FROM AUTHOR]

Understanding the role of surface morphology and molecular structure interface thermal transport is essential for designing thermal management materials. In the present work, models of solid–liquid interfaces were created by placing liquid n-alkane between two platinum crystals. The effect of different levels of crystal surface roughness–flat, small, and large-scale grooves–and polymer chain lengths, under varying solid–liquid affinity, on the interface thermal resistance (ITR) were assessed using non-equilibrium molecular dynamics simulations. The overall trend confirmed that grooved surfaces have higher ITR than flat surfaces at low affinity, and lower ITR values were observed at high affinity. Large grooves enabled more favourable polymer orientations than those of small grooves, resulting in a smaller ITR. However, long chains did not facilitate heat transfer normal to the interface because they preferentially aligned parallel to it. For efficient heat transfer, a balance between the roughness scale and polymer length must be considered. [ABSTRACT FROM AUTHOR]

With the continuous development of high‐end electronic information technologies such as 5G communications, thermal management is an urgent issue in the electronic and circuit industries due to the miniaturization, functionalization and integration. Recently, polymer‐based composites with the fillers of hexagonal boron nitride (h‐BN) have been regarded as promising candidates resulting from their excellent thermal conductivity (TC), good insulation and remarkable comprehensive properties. However, the high surface inertness of h‐BN itself, incompatibility with matrix and other fillers and mismatch of phonon‐spectrum will bring about the matrix/filler and filler/filler interfacial thermal resistance (ITR), which will greatly decline the TC of the composites, and limit their thermal management ability. Therefore, how to design, regulate and improve the interfacial states in composites and eventually enhance the TC is a current challenge. Researchers have made great effort to reduce the ITR of the composites to improve their TC. However, a comprehensive summary and analysis of researches on the improvement methods of the interface states in composites in the past 3 years is still lacking. In this work, the commonly used mechanism models, and simulation methods for calculating and predicting TC was summarized. From perspectives of Synthesis of h‐BNNs, modification, orientation, bridging and three‐dimensional structures construction, we reviewed strategies for improving the interface states in composites, and focused on the ITR regulation and TC improvement. The improvement effects of various methods on TC were compared. The development trend of high TC composite materials was prospected. Highlights: Crystallinity, defect, size, flatness, thickness of hexagonal boron nitride nanosheets (BNNSs) affect interfacial thermal resistance (ITR).Nature of interaction between adjacent layers of BNNS need exploited.Interface and defect are root cause of extra phonon scattering.Shape, density, surface area, distribution and compatibility reduce ITR.Theory, model, simulation methods need developed on different levels. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid development of nanotechnology, using the applied electric field to regulate interfacial heat transfer has become increasingly important. In the present work, the relationship between the thermal resistance of Kapitza and the direction of the applied electric field is explored with nonequilibrium molecular dynamics method at a solid–liquid interface consisting of CU (0, 0, 1) and liquid water. It found that the electric field orientation induces the ordering of water molecules near the solid, which affects the magnitude of the Kapitza thermal resistance. In addition, the electric field orientation affects the degree of mismatch between solid and liquid vibrational dynamical density (VDOS), which affects the phonon transport at the solid–liquid interface, and ultimately affects the process of interfacial heat transfer. Furthermore, it's found that there is a weak correlation between the interfacial thermal resistance and the dimension of the copper-water model. [ABSTRACT FROM AUTHOR]

Ceramic‐based polymer composites are commonly utilized as thermal management materials due to their high thermal conductivity and electrical insulation properties. One efficient method to enhance the thermal conductivity of these composites is by constructing a three‐dimensional thermal conductive network within the polymer matrix. In this study, alumina was coated onto the surface of polyurethane (PU) foam, followed by high‐temperature removal of the PU foam and sintering of the alumina sheets to obtain a continuous alumina framework. Epoxy resin was then infiltrated into this alumina framework to fabricate highly thermally conductive EP/f‐Al2O3 composites. The EP/f‐Al2O3 composite achieved a thermal conductivity of 2.44 W m−1 K−1 when the filler content of 26.8 vol%, representing a 400% improvement compared to EP/Al2O3 composite with randomly dispersed fillers, and a remarkable 1180% enhancement compared to epoxy resin. Infrared thermal imaging also confirmed the excellent heat dissipation capability of the EP/f‐Al2O3 composites. Overall, this research presents an effective method for producing highly thermally conductive and electrically insulating composites that can be used in electronic thermal management applications. Highlights: Fabrication of porous Al2O3 frameworks/epoxy composites.Porous Al2O3 frameworks were fabricated by polyurethane foam template.The obtained EP/f‐Al2O3 composite exhibited excellent thermal conductivity. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) reinforced polymer nanocomposites with high thermal conductivity show a promising prospect in thermal management of next‐generation electronic devices due to their excellent mechanical adaptability, outstanding processability, and superior flexibility. However, interfacial thermal resistance between individual CNT significantly hinders the further improvement in thermal conductivity of CNT‐reinforced nanocomposites. Herein, an interfacial welding strategy is reported to construct graphitic structure welded CNT (GS‐w‐CNT) networks. Notably, the obtained GS‐w‐CNT/polydimethylsiloxane (PDMS) nanocomposite with a GS loading of 4.75 wt% preserves a high thermal conductivity of 5.58 W m−1 K−1 with a 410% enhancement as compared to a pure CNT/PDMS nanocomposite. Molecular dynamics simulations are utilized to elucidate the effect of interfacial welding on the heat transfer behavior, revealing that the GS welding degree plays an important role in reducing both phonon scattering in the GS‐w‐CNT structure and interfacial thermal resistance at the interfaces between CNT. The unique welding strategy provides a new route to optimize the thermal transport performance in filler reinforced polymer nanocomposites, promoting their applications in next‐generation microelectronic devices. [ABSTRACT FROM AUTHOR]

The thermoreflectance technique is one of the few methods which can measure thermal diffusivity of thin films as thin as 100 nm or thinner in the cross-plane direction. The thermoreflectance method under rear-heat front-detect configuration is sometimes called ultrafast laser flash method because of its similarity to laser flash method. Up to now it has typically only been possible to attempt to evaluate the interfacial thermal resistance between the thin films by preparing and measuring several samples with different thicknesses. In this study, a method to directly determine interfacial thermal resistance by a single measurement of a thin film on substrate is represented, by analyzing the shape of thermoreflectance signals with analytical solutions in frequency domain and time domain. Thermoreflectance signals observed from metallic thin films on sapphire substrate with different thickness steps were analyzed by Fourier analysis and fitted by analytical equations with four parameters: heat diffusion time across the first layer, ratio of virtual heat sources, characteristic time of cooling determined by interfacial thermal resistance and relative amplitude of the signal. Interface thermal resistance between the thin film and substrate was able to be determined reliably with smaller uncertainty. [ABSTRACT FROM AUTHOR]

The present study focuses on the computation of the distribution of local solid–liquid interfacial thermal resistances (ITRs) at a solid–liquid interface with a nanostructured surface, at a spatial resolution of 1.96 10-1nm based on the non-equilibrium molecular dynamics method. As a calculation parameter, three different interaction strengths between the solid atoms and the liquid molecules were employed to reproduce the hydrophobic and hydrophilic conditions. In our calculation system, liquid molecules occupy the gap between the sidewalls of the nanostructure. We showed that the combined interfacial thermal resistance calculated from the local ITRs agrees with the overall ITR. We investigated the spatial distribution of the local ITRs via spectral analysis. The results showed that the local ITRs increased at the bottom corners and decreased at the top corners of the nanostructure. When the interaction parameter between the solid atoms and the liquid molecules is large, we find evidence of adsorption of liquid molecules on the solid, which causes fluctuations of the local ITR. The local vibrational states of the solid atoms and liquid molecules varied at each local interface. The local ITRs were negatively correlated with the overlaps of these vibrational densities of states, implying that each local vibrational state is one of the factors that determines the corresponding local ITR. In addition, the peak frequencies of the local spectral heat flux agreed with those of the vibrational density of states. These results indicate that the vibrational states of the solid atoms are dominant factors in the vibrational properties of the thermal transport across the local solid–liquid interfaces.

Abstract In this paper, molecular dynamics simulations have been employed to investigate the phonon thermal transport in bilayer polycrystalline graphene nanoribbon (pGNR/pGNR), compared with bilayer graphene nanoribbon (GNR/GNR) and pGNR/GNR heterostructure. The interfacial thermal resistance (ITR) of bilayer structures was also calculated using the heat dissipation method. The effects of interlayer interaction, grain size, and vacancy defects on ITR and in-plane phonon thermal conductivity of bilayer structures were investigated. It was found that the ITR as well as in-plane phonon thermal conductivity of pGNR/pGNR was less than that of pGNR/GNR and much less than that of GNR/GNR, for the same size. For the studied bilayer structures, both the ITR and in-plane phonon thermal conductivity decrease with increasing interlayer interactions. Moreover, ITR increases with increasing grain area size whereas decreases with increasing vacancy defects in pGNR-based bilayers. The introduction of pGNR interface roughness and vacancy defects results in an enhanced phonon coupling in pGNR-based bilayers compared to pure GNR/GNR bilayers. Presented simulation investigations will help to understand the interlayer thermal transport properties of polycrystalline graphene and provide essential guidance for experimentally regulating phonon thermal transport between layers of polycrystalline graphene.

AbstractMulti-walled carbon Nanotube (MWCNT) fillers are extensively used to improve the thermomechanical properties of polymers. In this study, five different weight fractions (0%, 0.25%, 0.50%, 0.75%, and 1%) of MWCNT-polymer nanocomposites were prepared by the solution mixing technique. The thermal conductivity of MWCNT-polymer nanocomposites was investigated using the laser flash method. The closed-form solution of the modified Mori-Tanaka homogenization method was developed for the accurate estimation of the thermal conductivity of nanocomposite materials after considering the influence of interfacial thermal resistance (ITR). The finite element simulation of RVE modelling was utilized to predict the thermal conductivity of nanocomposites with and without consideration of the interfacial thermal resistance effect. A perfect bond was assumed between MWCNT and polymer for both numerical and analytical studies. The thermal conductivity results obtained from the closed-form solution of the modified Mori-Tanaka method were in good agreement with both the finite element simulation (FEM) and experimental results.

Two-dimensional (2D) materials have attracted more and more attention due to their excellent properties. In this work, we systematically explore the heat transport properties of Graphene-C3B (GRA-C3B) superlattices and van der Waals (vdW) heterostructures using molecular dynamics method. The effects of interface types and heat flow directions on the in-plane interfacial thermal resistance (ITRip) are analyzed. Obvious thermal rectification is detected in the more energy stable interface, GRA zigzag-C3B zigzag (ZZ) interface, which also has the minimum value of ITRip. The dependence of the superlattices thermal conductivity (k) of the ZZ interface on the period length (l p ) is investigated. The results show that when the l p is 3.5 nm, the k reaches a minimum value of 35.52 W m−1 K−1, indicating a transition stage from coherent phonon transport to incoherent phonon transport. Afterwards, the effects of system size, temperature, coupling strength and vacancy defect on the out-of-plane interfacial thermal resistance (ITRop) are evaluated. With the increase of temperature, coupling strength and vacancy defect, ITRop are found to reduce effectively due to the enhanced Umklapp phonon scattering and increased probability of energy transfer. Phonon density of states and phonon participation ratio is evaluated to reveal phonon behavior during heat transport. This work is expected to provide essential guidance for the thermal management of nanoelectronics based on 2D monolayer GRA and C3B. [ABSTRACT FROM AUTHOR]

The effect of variation in the Si/Al interface structure on the thermal properties is explored with nonequilibrium molecular dynamics method in present work, and two distinct approaches are employed to manipulate the interface structure. The first is to change the arrangement of the atoms in the Al region by changing the orientation of the axis. The second one is to dig out several layers of atoms near the Al interface, so that the interface appears as a groove-like defect with different depths. Both methods exhibit a direct impact on atomic surface density. The high atomic surface density indicates a more compact atomic arrangement inside the structure, which improves the heat transport. In addition, the internal mechanism of thermal resistance change is probed from the aspects of Grain Boundary (GB) energy, vibrational density of states (VDOS) and the overlap of phonon spectrums parameter. It is found that structures with high atomic surface density correspond to smaller GB energies and larger overlap of phonon spectral parameters. Furthermore, by comparing the two ways of changing the interface structure, it is found that changing the degree of interface defects has a larger effect on the interfacial thermal resistance. [ABSTRACT FROM AUTHOR]

AbstractBy coating a heat transfer surface with a thin film, we can improve the heat and mass transfer as in the case of micro heat pipes. This study investigates the effects of periodic defective graphene on the density depletion length and the interfacial thermal resistance at the liquid–solid interface through a nonequilibrium molecular dynamics simulation of a water–graphene–Cu system. The results show that the defect concentration of thin graphene plays an essential role in the interfacial thermal resistance. Specifically, it determines the relationship between the density depletion length and the interfacial thermal resistance between water and solid surfaces. In contrast to a pristine graphene coating, a periodic defective graphene coating affects the density depletion length, while the interfacial thermal resistance at the copper–liquid interface decreases clearly with the defect concentration at the strong interaction strength between thin graphene and water. [ABSTRACT FROM AUTHOR]

Phase change memories (PCRAM) are often made of chalcogenide alloys in the form of multilayer systems (MLS). The mostly used alloys are Ge2Sb2Te5 and Ge‐rich Ge2Sb2Te5. The current article reports on the thermal characterization of very thin (<5 nm) Ge‐rich Ge2Sb2Te5/Ge2Sb2Te5 MLS by modulated photothermal radiometry (MPTR). The MPTR method allows for the investigation of such samples by determining, with an inverse method, the total thermal resistance of the stack deposited on the substrate. With the measurement of the total thermal resistance, it is possible to determine the thermal conductivity of the deposit and the interfacial thermal resistances between layers. The interfacial thermal resistance between Ge‐rich Ge2Sb2Te5/Ge2Sb2Te5 is characterized, which is an important parameter to reduce the energy cost of the PCRAM functioning. It is also possible to highlight a decrease in interface quality inside the MLS after the beginning of the phase transition around 250 °C. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Multi-walled carbon Nanotube (MWCNT) fillers are extensively used to improve the thermomechanical properties of polymers. In this study, five different weight fractions (0%, 0.25%, 0.50%, 0.75%, and 1%) of MWCNT-polymer nanocomposites were prepared by the solution mixing technique. The thermal conductivity of MWCNT-polymer nanocomposites was investigated using the laser flash method. The closed-form solution of the modified Mori-Tanaka homogenization method was developed for the accurate estimation of the thermal conductivity of nanocomposite materials after considering the influence of interfacial thermal resistance (ITR). The finite element simulation of RVE modelling was utilized to predict the thermal conductivity of nanocomposites with and without consideration of the interfacial thermal resistance effect. A perfect bond was assumed between MWCNT and polymer for both numerical and analytical studies. The thermal conductivity results obtained from the closed-form solution of the modified Mori-Tanaka method were in good agreement with both the finite element simulation (FEM) and experimental results. [ABSTRACT FROM AUTHOR]

Highlights: The flexible composite film presents ultrahigh thermal conductivity and good thermal management performance in electronic devices. An original "self-modified nanointerface" strategy is used to reduce the interfacial thermal resistance between boron nitride and the polymer matrix. The ideal phonon spectrum matching between boron nitride nanocrystals and fillers as well as the strong interaction between self-modified fillers and the polymer matrix are the two major contributors to decrease the interfacial thermal resistance. While boron nitride (BN) is widely recognized as the most promising thermally conductive filler for rapidly developing high-power electronic devices due to its excellent thermal conductivity and dielectric properties, a great challenge is the poor vertical thermal conductivity when embedded in composites owing to the poor interfacial interaction causing severe phonon scattering. Here, we report a novel surface modification strategy called the "self-modified nanointerface" using BN nanocrystals (BNNCs) to efficiently link the interface between BN and the polymer matrix. Combining with ice-press assembly method, an only 25 wt% BN-embedded composite film can not only possess an in-plane thermal conductivity of 20.3 W m−1 K−1 but also, more importantly, achieve a through-plane thermal conductivity as high as 21.3 W m−1 K−1, which is more than twice the reported maximum due to the ideal phonon spectrum matching between BNNCs and BN fillers, the strong interaction between the self-modified fillers and polymer matrix, as well as ladder-structured BN skeleton. The excellent thermal conductivity has been verified by theoretical calculations and the heat dissipation of a CPU. This study provides an innovative design principle to tailor composite interfaces and opens up a new path to develop high-performance composites. [ABSTRACT FROM AUTHOR]

Diamond/SiC composites have long been recognized as advanced materials for thermal management as they exhibit excellent thermal and mechanical properties. The objective was to investigate and understand the phase composition, diamond graphitization behavior, microstructure, and properties of diamond/SiC composites developed following the liquid silicon infiltration process. The results revealed that the incorporation of α-SiC particles increased the degree of uniformity of the microstructure of the diamond/SiC composites. The acoustic mismatch model was used to analyze the samples before and after diamond graphitization to evaluate the interfacial thermal resistance of the composites. The results indicated that the interfacial thermal resistance of the graphitized composites was 11.9 times higher than the interfacial thermal resistance of the un-graphitized composites. Finally, the correlation between the diamond content of the composites and their thermal and mechanical properties was investigated. [ABSTRACT FROM AUTHOR]

Continued miniaturization of microelectronics has led to increased energy and interface density within those electronics. With each new interface, a new thermal resistor is created, preventing heat from efficiently escaping the device. This is such a problem that Kapitza resistance or thermal boundary resistance is now the dominant cause of thermal resistance in most microelectronics. Thermal boundary resistance has been studied extensively. However, thermal boundary resistance remains poorly understood. In this review, the existing literature is critically looked at, focusing on molecular dynamic simulations of the Si/Ge interface, which has become the de facto standard against which most other methods and systems are compared. As such, the volume of literature available on this system is considerably larger than any other, and the depth of analysis that can be performed is far greater. A research strategy for the field is presented to maximize progress in controlling Kapitza resistance. It is proposed that benchmark systems need to be found so that calculations can be properly verified, and that the size effects on Kapitza resistance need to be fully characterized. Finally, strong evidence is presented that first‐principles calculations offer the best chances for meaningful future progress, preferably with anharmonic contributions intact. [ABSTRACT FROM AUTHOR]

The thermal conductivity of energy-containing materials has a significant impact on their environmental suitability during manufacturing, transportation, and storage. In order to effectively regulate the thermal conductivity of polymer-bonded explosives (PBXs), this study investigates the effects of different aspect ratios of graphene binder and interfacial thermal resistance on the thermal conductivity of TATB-based PBXs using the finite element method. A model was constructed using Abaqus software to establish the constitutive relationship between graphene with varying aspect ratios and the thermal conductivity of PBXs. The results indicate that the effect of different graphene aspect ratios on the overall thermal conductivity of PBXs is small when the graphene content is lower than 3%. However, the thermal conductivity of PBXs increases nonlinearly with the increase in graphene aspect ratio when the graphene content is higher than 8%. Furthermore, the interfacial thermal resistance reduces the thermal conductivity of the PBX system by approximately 0.16 W/(m K), and its effect on the thermal conductivity of the system is relatively stable and does not change significantly with increasing graphene content and aspect ratio. [ABSTRACT FROM AUTHOR]

● The Gd/Cu bimetal composites are fabricated and interfacial layers are observed. ● Interfacial thermal resistance (ITR) is calculated based on thermal resistance test. ● Equivalent thermal conductivity is proposed to evaluate heat transfer capability. ● Reducing the ITR can significantly improve solid-state magnetic cooling performance. ● Combination of a topology-optimized structure and a reduced ITR is more beneficial. The low heat transfer efficiency caused by a magnetocaloric material (MCM) with low thermal conductivity is the bottleneck that limits the performance of magnetic refrigeration (MR). Previous studies have shown that a bimetal composite of a high thermal conductivity material and an MCM is effective in improving the heat transfer rate. However, the bimetal composite structure causes extra interfacial thermal resistance (ITR). Therefore, this study investigates the processing of gadolinium/copper bimetal composites by fusion casting and experimentally determines the ITR. To evaluate the structural heat transfer capability, the equivalent thermal conductivity (k eq) is proposed, which is calculated based on the ITR result and simulation. The influence of the ITR and k eq on the cooling performance of a fully solid-state MR is carefully investigated using a validated simulation model. The results show that the smallest ITR of 3.74 × 10−5 m2 K W −1 is obtained with a copper pouring temperature of 1200 °C owing to the thinnest bonding interfacial layer. The topology-optimized structure, using the ITR obtained by fusion casting, has an k eq of 159.8 W m −1 K −1, with an increase of 39% compared to the structure assembled with thermal grease. As a result, the maximum specific cooling power (SCP max) range and corresponding optimal operating range are significantly expanded to 45.6–209.3 W kg−1 and 0.23–0.61 rpm, respectively, with an average SCP max increase of 35.5%. The combination of using topology optimization design to reduce the structural thermal resistance and using a suitable forming process to reduce the ITR can be more beneficial to the performance improvement of solid-state MR. [ABSTRACT FROM AUTHOR]

Considering the importance of high‐performance composite phase change materials (PCMs) for the realization of efficient thermal energy storage, molecular dynamics simulations were conducted in this study to investigate the thermal properties of graphene/palmitic acid composites and the related interfacial thermal transport. The effects of the interactions between functionalized graphene and fatty acids on the thermal transport properties needs to be investigated further. The addition of functionalized graphene (with epoxy, hydroxyl, and carboxyl groups) increased the phase transition temperature and decreased the specific heat capacity of the PCM, whereas both of these parameters increased with increasing functional group coverage (FGC). Further the effects of the FGC and functional group type on the interfacial thermal resistance (ITR) were investigated by analyzing the interaction energy and vibrational density of states, and the ITR decreased with increasing FGC. Compared to that of pure PA, the phase‐transition temperatures of the PA/pristine graphene composites were higher by ~7 K. The ability of functional groups to decrease the ITR decreased in the order of epoxy < hydroxyl < carboxyl at a constant FGC of 10.12%, with the ITR decreasing by 31.26%, 44.77%, and 56.41%, respectively. The obtained insights are expected to facilitate the design of high‐performance energy storage systems based on composites of fatty acids as PCMs. Highlights: Thermal transport in functionalized graphene/palmitic acid composites is studied.Effects of functional group type/coverage on composite thermal properties are probed.Molecular dynamics simulations are used for thermal property analysis.The obtained insights promote the design of high‐performance phase‐change materials. [ABSTRACT FROM AUTHOR]

The roughness and film thickness effects on the interfacial thermal resistance (ITR) are explored at two deliberately selected temperatures in use of Monte-Carlo simulation method. Particular methods are proposed to define properly the phonon emitting temperature based on the one-way deviational heat flux, and to define correctly the phonon equilibrium temperature by considering the different properties and residence times of incident, transmitted, and reflected phonons near an interface. A mixed mismatch model which allows polarization conversion is constructed and employed. The so-obtained traditional ITRs, defined based on the emitting temperature difference, and the revised ITRs, defined based on the equilibrium temperature difference, are compared with model predictions in the literature. Simulation results show that at high temperature the revised ITR decreases monotonically with increasing film thickness and at low temperature it possesses a local minimum against the interface roughness. The latter is explained by the monotonically increasing traditional ITR and monotonically decreasing ratio of the equilibrium temperature difference to emitting temperature difference with increasing roughness. Among all the studied models, only the newly proposed one can well predict the ITR for different interface roughness at low temperature. None of the models captures the monotonic decrease of ITR with film thickness at high temperature however. [ABSTRACT FROM AUTHOR]

Epoxy composites are increasingly employed in the information industry fields, where the interfacial thermal resistance of polymer/nanofiller is considered to be one of the most important factors affecting the thermal conductivity of polymer composites. Herein, the interfacial thermal resistance with different functionalized aluminas and epoxy is first investigated by molecular dynamics. The functional groups considered in aluminas are –OH, butyltrimethoxysilane terminating with –CH3, and aminopropyltriethoxysilane terminating with –NH2. The results indicate that aminopropyltriethoxysilane terminating with –NH2 has the best effect on reducing the interfacial thermal resistance up to 66.67%. The mechanism of interfacial thermal resistance reduction is analyzed through vibrational density of state and overlapping energy, and then the effect of functionalization on interfacial heat transfer is intuitively demonstrated through local thermal analysis. The most effective reduction of the thermal resistance is attributable to the functional groups containing the same group end group as epoxy and the moderate chain length, which can reduce the vibrational mismatch and form more effective heat conduction channels to enhance the thermal transport efficiency in the nanocomposite. This work can shed some light on designing and fabricating thermally conductive inorganic/polymer composite. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights The flexible composite film presents ultrahigh thermal conductivity and good thermal management performance in electronic devices. An original “self-modified nanointerface” strategy is used to reduce the interfacial thermal resistance between boron nitride and the polymer matrix. The ideal phonon spectrum matching between boron nitride nanocrystals and fillers as well as the strong interaction between self-modified fillers and the polymer matrix are the two major contributors to decrease the interfacial thermal resistance.

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. [ABSTRACT FROM AUTHOR]

The demands for effective thermally conductive dielectric composite materials continue to increase due to high speed and low-loss signal propagation required in microwave frequency applications. Composites of polytetrafluoroethylene (PTFE) and boron nitride are promising for these applications. Here, for the first time, recent generation surface-engineered boron nitride nanobarbs (BNNB) material was evaluated at a low filler content in PTFE to achieve the desirable high thermal conductivity and low dielectric loss requirements which are typically difficult without a strong filler–matrix interaction and high filler loading. Composites of modified BNNB and modified PTFE were also fabricated and evaluated. These composites exhibited higher thermal conductivity (1.2–1.3 W/mK) with a lower concentration of boron nitride nanoparticles than those reported in the literature. The data were analyzed by theoretical models and interfacial thermal resistance was the lowest for the composite made from the modified PTFE and modified BNNB. Additionally, the composites displayed excellent dielectric properties including a dielectric constant ≈2.3 and loss tangent of less than 0.005 at frequencies of 1–3 GHz. These results indicate that such thermally conductive and low-loss dielectric composites have significant potential as materials for thermal management and dielectric components in microelectronics, 5G, and microwave devices. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIM) represented by submicron silver adhesive provide a promising solution for ultra‐high heat dissipation in chip integration. However, it is difficult to accurately characterize the thermal performance of submicron silver adhesive interfaces, and their high‐temperature degradation mechanism still remains unclear. Herein, the accelerated high‐temperature aging experiments of submicron silver adhesion interfaces are performed, and a non‐destructive testing method is provided to measure the degeneration of interfacial thermal resistance (ITR). After performing the two‐sided test, ITR can be extracted with an error of less than 4.6%. Based on scanning electron microscopy and X‐ray microstructural analysis, the microstructural evolution of silver adhesive interfaces is presented and its high‐temperature degradation mechanism is determined. It is observed for the first time that ITR would change with the aging time following a bathtub curve. Such a degenerative process can be evidently divided into three stages including secondary solidification, fluctuation, and failure. In addition, a physical model is developed to interpret the degradation mechanism of ITR at high temperatures. The change in the trend of submicron silver body and TIM–solid contact thermal resistance at different stages is presented. This work helps promote submicron silver's application as high‐performance TIM. [ABSTRACT FROM AUTHOR]

We have developed an experimental method to extract interfacial thermal resistance (ITR) at an organic/semiconductor interface based on optical-interference contactless thermometry. The proposed technique was applied to a SU-8/SiC bilayer sample, and clear oscillations in reflectivity induced by optical interference during pulse heating and cooling were observed. After fitting the observed reflectivity waveform with simulation results by a two-dimensional (2D) double-layer heat conduction model and multi-reflection calculations, ITR was extracted as 190 mm ^2 K W ^−1 , which resulted in a temperature drop of 11 K at the interface. Moreover, the 2D transient temperature distribution of the sample throughout pulse heating and cooling was obtained.

As a semiconducting material with relatively low thermal conductivity, MoS2 nanoflake has the potential to serve as a modulator for optimizing the performance of thermoelectric (TE) materials. However, the low yield of MoS2 nanoflakes prepared by conventional methods has constrained the development of MoS2 optimized TE materials. We propose a mechanical exfoliation method for mass production of MoS2 nanoflakes using attrition mill. After mixed with La and Nb co-doped SrTiO3 (SLNT) powder, the MoS2/SLNT composites are fabricated by spark plasma sintering. It is found that the heterojunctions formed at MoS2/SLNT interfaces with proper band offset can effectively scatter the low-energy electrons, resulting in enhanced Seebeck coefficient without significantly undermining the electrical conductivity. The power factor of composites is improved when the MoS2 content is lower than 1.5 vol%. Meanwhile, the thermal conductivity of composites is significantly decreased due to the phonon scattering induced large thermal resistance at MoS2/SLNT interfaces, which is much higher than that in graphene embedded SrTiO3 composites. Consequently, a maximum ZT = 0.24 is obtained at 800 K in 1.5 vol% MoS2/SLNT composite, which is ∼26 % higher compared with pristine matrix. This work paves the way for application of TE materials modulated by transition metal dichalcogenides.

Abstract Thermal interface materials (TIM) represented by submicron silver adhesive provide a promising solution for ultra‐high heat dissipation in chip integration. However, it is difficult to accurately characterize the thermal performance of submicron silver adhesive interfaces, and their high‐temperature degradation mechanism still remains unclear. Herein, the accelerated high‐temperature aging experiments of submicron silver adhesion interfaces are performed, and a non‐destructive testing method is provided to measure the degeneration of interfacial thermal resistance (ITR). After performing the two‐sided test, ITR can be extracted with an error of less than 4.6%. Based on scanning electron microscopy and X‐ray microstructural analysis, the microstructural evolution of silver adhesive interfaces is presented and its high‐temperature degradation mechanism is determined. It is observed for the first time that ITR would change with the aging time following a bathtub curve. Such a degenerative process can be evidently divided into three stages including secondary solidification, fluctuation, and failure. In addition, a physical model is developed to interpret the degradation mechanism of ITR at high temperatures. The change in the trend of submicron silver body and TIM–solid contact thermal resistance at different stages is presented. This work helps promote submicron silver's application as high‐performance TIM.

A series of finite element analyses were conducted to clarify the effect of contact and interfacial resistance between constituents on effective thermal conductivities of dispersed composites. Equally dispersed fillers in FCC (face-centered cubic) and BCC (body-centered cubic) material systems were extracted from cyclic microstructures as unit cell models. In addition to spherical fillers, a polyhedron called the Wigner–Seitz cell that can realize a fully packed microstructure was chosen as the shape of the filler to investigate the effect of contact between the high volumetric fraction of fillers. The effective thermal conductivities of the resulting composites were calculated based on the FEA results and compared to the theoretical results for various volume fractions of the fillers including the maximum packing fraction. The following conclusions were obtained from the present study: 1. The effect of the contact depending on the shape and configuration of the fillers has more of a significant influence on the effective thermal conductivity than the influence of the increase in the volume fraction of the fillers. 2. When the contact occurred, the effective thermal conductivity became more than double that without contact. 3. Interfacial thermal resistance must be less than the order of 10−4 m2 K/W to obtain improvement in the effective thermal conductivity by compounding the fillers. [ABSTRACT FROM AUTHOR]

Agglomeration of carbon nanotubes (CNTs) is a key phenomenon that affects the effective thermal conductivity of CNT-polymer nanocomposites. This issue needs to be adequately studied especially in the practice of prediction of the effective thermal properties of CNT nanocomposites. In this study, we developed a multiscale model within the framework of effective medium theory to predict the effect of CNT agglomeration on the overall thermal conductivity of the hierarchical CNT-polymer nanocomposite system over a wide range of CNT loading. With an introduced Cauchy cumulative probability function, we developed a new model of CNT agglomeration wherein the CNT volume fraction progressively evolves with the total loading of the CNT fillers in the composite. This model is self-consistent and it leads to a very good agreement with experimental observations. The entire multiscale approach consists of the newly developed model of the progressive agglomeration as well as models that altogether take into account the effect of two types of CNT interfacial thermal resistance and the unique feature of the CNT nanostructure. We highlighted this multiscale approach with its implementation in the prediction of the overall thermal conductivity. Good agreement was confirmed between the prediction and the experimental data. The study shows that the existence of CNT agglomerates downgrades the thermal percolation networks and it can cause a decrease up to 50% in the overall thermal conductivity of the nanocomposite. Two important parameters for the progressive agglomeration model were identified and their influences to the predicted results were examined. [Display omitted] [ABSTRACT FROM AUTHOR]

The trend toward miniaturization, integration and multifunctionality of modern electronics has led to a rapid increase in power density, which makes heat dissipation a critical issue. Despite the great potential of graphite-related nanocomposites in dissipating excess heat to ensure high efficiency and long lifetime of electronic devices, the practical application of these composites is limited by the ultra-low vertical thermal conductivity due to the interfacial thermal resistance between graphite layers. Here, a caterpillar-like hybrid filler was fabricated by the in situ intercalation of boron nitride nanotubes (BNNTs) between expanded graphite (EG) layers based on chemical vapor deposition technology. Owing to the optimized interfacial thermal resistance by forming covalent C-N bonding at the interface of EG and BNNT, the through-plane thermal conductivity of epoxy-based nanocomposites can be up to 5.18 Wm−1 K−1. In addition, the composite possessed electromagnetic interference shielding performance of 33.34 dB while maintaining electrical insulation due to the hierarchical structure. This work provided a new strategy for fabricating polymer-based composites with excellent through-plane thermal conductivity in thermal management applications. [ABSTRACT FROM AUTHOR]

In this study. the measurement of thermal conductivity and interfacial thermal resistance between the microheater and polydimethylsiloxane (PDMS) with different surface roughness is measured by the bidirectional 3ω method. The PDMS samples with a different surface roughness of arithmetic average of roughness profile ranging from 0.29 to 2.58 µm are considered. Maximum pressure of 250 kPa between PDMS and 3ω sensor is applied to manipulate the interfacial thermal resistance between the sample and the 3ω sensor. Comparison of measured and theoretically calculated temperature amplitudes are made to fit the thermal conductivity of PDMS and interfacial thermal resistance at the heater-sample interface. The thermal conductivity of PDMS is found to agree well with the literature value. The interfacial thermal resistance between the PDMS and microheater ranged from 4.5 x 10-7 to 8.7 x 10-7 m²K/W. [ABSTRACT FROM AUTHOR]

Graphene is a two-dimensional material that can be folded into diverse and yet interesting nanostructures like macro-scale paper origami. Folding of graphene not only makes different morphological configurations but also modifies their mechanical and thermal properties. Inspired by paper origami, herein we studied systemically the effects of creases, where sp2 to sp3 bond transformation occurs, on the thermal properties of graphene origami using molecular dynamics (MD) simulations. Our MD simulation results show that tensile strain reduces (not increases) the interfacial thermal resistance owing to the presence of the crease. This unusual phenomenon is explained by the micro-heat flux migration and stress distribution. Our findings on the graphene origami enable the design of the next-generation thermal management devices and flexible electronics with tuneable properties.

We experimentally investigate the near-wall heat transfer at single bubble growth in nucleate saturated pool boiling of water at atmospheric pressure. Our focus is on the evaporation of the micro-metric thin film of liquid (microlayer) that is formed between the heating wall and the bubble. High speed and high resolution optical techniques are employed. Synchronous and simultaneous measurements of the microlayer thickness, wall temperature and bubble macroscopic shape are performed by white light interferometry, infrared thermography and side-wise shadowgraphy, respectively. We measure the wall temperature of an ITO heating film through a transparent to the infrared waves porthole. The heating is provided by an infrared laser. The wall heat flux is numerically reconstructed by using the experimental wall temperature data. We reveal a temporal rise of the thermal resistance of the liquid–vapor interface during the microlayer evaporation, which corresponds to a decrease of the accommodation coefficient. We attribute it to the progressive accumulation of impurities at the interface during evaporation. The contribution of microlayer evaporation to the overall bubble growth is about 18%. • Advanced optical techniques are used to investigate the microlayer evaporation. • Microlayer thickness and wall temperature distribution are measured synchronously. • Wall heat flux is reconstructed from wall temperature distribution. • Interfacial thermal resistance increases over time during microlayer evaporation. [ABSTRACT FROM AUTHOR]

• The measurement sensitivity is defined as the percent change in normalized Raman shift power coefficient with a 10 % increase in interfacial thermal resistance. The sensitivity is investigated using 3D transient thermal transport simulations by COMSOL. • The measurement sensitivity increases with increased frequency, a range of 500 kHz -1 MHz is recommended to promise high measurement sensitivity for MoS 2 /SiO 2. • The measurement sensitivity increases first, then decreases with increased laser spot radius. A range of 1-2 μm is recommended to reduce the measurement error. • The thickness of oxide layer has significant effect on the measurement sensitivity of MoS 2 /SiO 2 /Si. Oxide layer with 1000 nm thickness can ensure high measurement sensitivity. Opto-thermal Raman-based technique is widely used for measuring the interfacial thermal resistance ( R ″ t c) between 2D materials and substrate due to its high spatial resolutions. Frequency-domain energy transport-resolved Raman (FET-Raman) has been developed to characterize R ″ t c without the need of Raman shift temperature coefficient and laser absorption coefficient. The FET-Raman constructs two energy transport states: steady state and transient state by employing a continuous wave laser and frequency-modulated laser to differentiate the contribution of R ″ t c to the total thermal resistance under two energy transport states. This work discusses the effect of time and spatial domains on the interfacial thermal resistance measurement by a 3D heat conduction simulation in MoS 2 supported by fused silica. By running multiple simulations for a range of modulation frequency, laser spot size, and laser absorption depth, the results reveal that higher modulation frequency results in higher R ″ t c measurement sensitivity. But the optimal modulation frequency leading to maximum measurement sensitivity depends on the laser spot size, and interfacial thermal resistance. For the SiO 2 /Si substrate, oxide layer thicker than 1000 nm can ensure the R ″ t c measurement sensitivity. [ABSTRACT FROM AUTHOR]

• Calculation of cross-scale anisotropic thermal transport in carbon fiber composites. • Use of the dual coordinate system to describe thermal conductivity anisotropy. • The mechanism of interface rotation affecting interfacial thermal resistance. • The heat transport properties of fiber tortuosity and orientation within the resin substrate were investigated. The thermal conductivity parameter of materials is a fundamental factor for thermal management and the study of heat transfer processes. In the present work, we constructed the microscopic topology and interfacial structure of the fiber structure based on the homogenization of finite elements and molecular dynamics theory. For the anisotropy of fiber thermal conductivity, we proposed an anisotropic cross-scale heat transport model for carbon fiber/epoxy resin (CF/ER) composites, with consideration of interfacial thermal resistance (ITR). Based on the numerical validation of the reliability of the method, we established a dual coordinate system to analyze the mechanism of the geometric topological parameters on the structural anisotropic heat transport. The fiber volume fraction significantly affected the effective thermal conductivity (ETC) within a range of 10% to 15%, with ETC growth rates of up to 50%. The fiber orientation angle influenced the main heat transfer direction, and when the fiber volume fraction was 40%, increasing the fiber orientation angle to 90° could enhance the ETC in the axial direction up to 130.28%. Meanwhile, the larger orientation angle could reduce the interfacial phonon heat dissipation and achieve the better phonon transmission effect. The change of fiber structure could effectively modulate the ETC, while the fiber length and cross-sectional shape would have less effect on the ETC. With the introduction of fiber tortuosity, the heat transport could be regulated by changing the tortuosity. Within the variation range of tortuosity from 1 to 3, the ETC regulation of the composite could be achieved from 12% to 42% in the axial direction and 14% to 34% in the radial direction. With increasing curvature, the ETC variation trend became gradually nonlinear. The study serves as a theoretical basis for the preparation and thermal properties evaluation of fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

• The interfacial thermal resistance between nm-thick MoS 2 nanosheets and Si substrate in the ambient temperature range from −60 °C to 50 °C is measured by using the ns energy transport state-resolved Raman (ns ET-Raman) technique. • As the environmental temperature deviates from room temperature, a large increasement of the interfacial thermal resistance can be observed. To understand the ITR-temperature trend, the ITR of mechanical exfoliated (in the order of 10−7 K m2 W−1), CVD grown (in the order of 10−8 K m2 W−1) and epitaxial materials (in the order of 10−9 K m2 W−1) were compared and discussed. • The uncertainty caused by several parameters in numerical simulations is studied to ensure the reliability of the measurement results, including the MoS 2 nanosheet sample size, the thermal conductivity of MoS 2 , and the thermal resistance of silicon wafer. In the miniaturization and integration development of micro-devices, the large thermal contact resistance significantly affects the overall performance of micro-devices, which is influenced by both interfacial contact condition and material properties. However, the temperature dependence of interfacial thermal resistance of realistic materials remains unclear. In this work, the interfacial thermal resistance between nm-thick MoS 2 nanosheets and Si substrate is measured by using the ns energy transport state-resolved Raman (ns ET-Raman) technique. By comparing the experimental data with finite difference numerical simulation, the real value of the interfacial thermal resistance is determined. By changing the ambient temperature from -60 °C to 50 °C, the interfacial thermal resistance against temperature curve is obtained. As the environmental temperature deviates from room temperature, a large increasement of the interfacial thermal resistance can be observed. As temperature goes back to room temperature, the unreversible interfacial thermal resistance indicates that the large thermal expansion mismatch deteriorates the contact situation. In the last, the interfacial thermal resistance evolution under varying environmental temperatures from both experiments and modeling results in literatures are compared and discussed to illustrate the effect of different interface formation methods. For epitaxial and CVD grown materials, the interfacial thermal resistance generally reduces with raising ambient temperature. While for mechanically exfoliated samples, the effect of thermal expansion mismatch and the resulting gaps dominate the interfacial thermal resistance, which leads to non-monotonous temperature dependency with a valley located at room temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

With the increased level of integration and miniaturization of modern electronics, high-power density electronics require efficient heat dissipation per unit area. To improve the heat dissipation capability of high-power electronic systems, advanced thermal interface materials (TIMs) with high thermal conductivity and low interfacial thermal resistance are urgently needed in the structural design of advanced electronics. Metal-, carbon- and polymer-based TIMs can reach high thermal conductivity and are promising for heat dissipation in high-power electronics. This review article introduces the heat dissipation models, classification, performances and fabrication methods of advanced TIMs, and provides a summary of the recent research status and developing trends of micro- and nanoscale TIMs used for heat dissipation in high-power electronics. [ABSTRACT FROM AUTHOR]

The mechanical properties and interfacial thermal resistance (ITR) of hybrid BC6N-BC2N structure are studied via molecular dynamics (MD) simulation. Different vacancy atoms type (B, N and C) dramatically affect the ITR and mechanical properties of hybrid BC6N-BC2N. When the vacancy defects are positioned throughout the entire or interface of hybrid structure, the ITR of hybrid structure increases. The effect of C atom vacancy defect on the ITR of hybrid structure is higher compared to others. The vacancy defects located along the interface have more influence on the ITR than those located throughout the entire of hybrid structure. Hybrid structure indicates high mechanical properties. The mechanical properties of hybrid structure are studied for various strain rates and temperatures. At high temperature, the strain rate effects on the mechanical properties of hybrid structure are more pronounced. Additionally, the effects of temperatures on the mechanical properties of hybrid structure rise at low strain rate. As the concentrations of defects increase to 3%, the mechanical properties of defective hybrid structure reduce. C atom vacancy defect demonstrates the most influence on the mechanical properties. Besides, the vacancy defects located throughout the interface have less influence on the mechanical properties than the ITR. [ABSTRACT FROM AUTHOR]