Search

This study presents an experimental measurement of interfacial thermal resistance (ITR) at polymer–polymer interfaces using a multi‐layered bulk sample approach. ITR is commonly measured using thin‐film techniques, but new advancements enable testing in bulk materials with multilayered structures. However, traditional multilayer fabrication is often resource‐intensive and lacks consistency. This study introduces a simple rotational overlapping method for fabricating multi‐layered polymer samples for bulk ITR measurement. Combining numerical simulations with experimental validation, researchers optimize layer overlapping conditions using measured viscosity data of high‐density polyethylene (HDPE), polypropylene (PP), and polylactic acid (PLA). Samples are fabricated at viscosity‐matching temperatures, and shear forces from stirring disks create uniform layer patterns. Computational fluid dynamics (CFD) simulations elucidate the layer formation mechanism, enabling the fabrication of samples with over 112 layers within a 4.6 mm thickness. ITR testing reveals a direct correlation between layer number and thermal resistance. PE‐PP samples exhibit an average ITR of 9.58 × 10−6 K m2 W−1, with a 10.32% increase in resistance from 38 to 112 layers. Similarly, PE‐PLA samples with an ITR of 1.31 × 10−5 K m2 W−1 show a 2.8% increase from 5 to 23 layers. Overall, The experimental procedure provides valuable data to advance the understanding of ITR in polymer–polymer interfaces. [ABSTRACT FROM AUTHOR]

The miniaturization, integration, and high data throughput of electronic chips present challenging demands on thermal management, especially concerning heat dissipation at interfaces, which is a fundamental scientific question as well as an engineering problem—a heat death problem called in semiconductor industry. A comprehensive examination of interfacial thermal resistance has been given from physics perspective in 2022 in Review of Modern Physics. Here, we provide a detailed overview from a materials perspective, focusing on the optimization of structure and compositions of thermal interface materials (TIMs) and the interact/contact with heat source and heat sink. First, we discuss the impact of thermal conductivity, bond line thickness, and contact resistance on the thermal resistance of TIMs. Second, it is pointed out that there are two major routes to improve heat transfer through the interface. One is to reduce the TIM's thermal resistance (RTIM) of the TIMs through strategies like incorporating thermal conductive fillers, enhancing interfacial structure and treatment techniques. The other is to reduce the contact thermal resistance (Rc) by improving effective interface contact, strengthening bonding, and utilizing mass gradient TIMs to alleviate vibrational mismatch between TIM and heat source/sink. Finally, such challenges as the fundamental theories, potential developments in sustainable TIMs, and the application of AI in TIMs design are also explored. [ABSTRACT FROM AUTHOR]

ABSTRACT Energy piles are commonly deployed in vertically layered geological conditions due to the geological structure and pile foundation backfill. The imperfect contact between adjacent soil layers results in resistance to heat transfer at the interface, known as the interfacial thermal resistance effect. In this paper, the energy pile was simplified as a finite‐length solid cylindrical heat source, and an analytical model was established for layered heat transfer of energy piles considering the interfacial thermal resistance effect. The Laplace‐domain solutions to the temperatures in the layered ground were derived by using the finite Hankel and Laplace transforms. The Crump method was subsequently employed to numerically invert Laplace‐domain solutions to the time‐domain solutions. The proposed model was validated by comparing with an analytical solution of a homogeneous model and COMSOL numerical solution. These solutions were used to analyze the temperature response around energy piles considering interfacial thermal resistance. Finally, a parametric study was performed to explore the effects of interfacial thermal resistance and other thermal properties of the soil layer on the layered heat transfer of energy piles. [ABSTRACT FROM AUTHOR]

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]

Abstract The miniaturization, integration, and high data throughput of electronic chips present challenging demands on thermal management, especially concerning heat dissipation at interfaces, which is a fundamental scientific question as well as an engineering problem—a heat death problem called in semiconductor industry. A comprehensive examination of interfacial thermal resistance has been given from physics perspective in 2022 in Review of Modern Physics. Here, we provide a detailed overview from a materials perspective, focusing on the optimization of structure and compositions of thermal interface materials (TIMs) and the interact/contact with heat source and heat sink. First, we discuss the impact of thermal conductivity, bond line thickness, and contact resistance on the thermal resistance of TIMs. Second, it is pointed out that there are two major routes to improve heat transfer through the interface. One is to reduce the TIM's thermal resistance (RTIM) of the TIMs through strategies like incorporating thermal conductive fillers, enhancing interfacial structure and treatment techniques. The other is to reduce the contact thermal resistance (Rc) by improving effective interface contact, strengthening bonding, and utilizing mass gradient TIMs to alleviate vibrational mismatch between TIM and heat source/sink. Finally, such challenges as the fundamental theories, potential developments in sustainable TIMs, and the application of AI in TIMs design are also explored.

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.

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]

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]

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.

The multilayer materials in aerospace applications generally subject to thermal shock, which may significantly affect the interfacial thermal resistance (ITR) and cause serious overheating issues. Therefore, understanding the interfacial thermal transport under temperature shock is essential for effective thermal management in aerospace devices. In the present study, the variation in ITR within the diamond/Cu/carbon nanotube tri-layer after thermal cycles was investigated through non-equilibrium molecular dynamics (NEMD) simulations. We conducted four groups of investigations, exploring the impact of maximum cycle temperature, heating/cooling rates, number of cycles, and interfacial structure on ITR. The results demonstrate that while the matching degree of phonon density of states remains almost constant, the ITR varies significantly among all groups. The structural deformations and changes in lattice type can be observed in the Cu layer. Based on these findings, we proposed an "atomic distribution method" to elucidate the mechanism behind ITR variation, which was verified as applicable and precise. Additionally, the thermal rectification results demonstrate the significant effect of interfacial structure on the rectification coefficient, indicating that interfacial transport and lattice thermal conduction deserve more in-depth study in the future. This work provides a novel perspective on understanding thermal transport across the irregular and complex interfaces, which is significant for the thermal management in aerospace field. [ABSTRACT FROM AUTHOR]

Interfacial thermal resistance plays a pivotal role in thermal management applications, including efficient heat dissipation, energy harvesting from waste heat, and thermal barrier coatings. This study delves into the thermal resistance characteristics of a SiGe phononic material layer, positioned between two Si or Ge thermostats (Si/SiGe/Si and Ge/SiGe/Ge). We discover that the lateral period of the phononic crystal W p , which is oriented perpendicular to the direction of thermal transport, can be used as an additional parameter to modulate thermal resistance. Notably, we observed distinct transport behaviors across phononic interfaces with varying W p in ballistic and diffusive transport regimes. In the ballistic limit, particularly in thinner layers, the thermal resistance diminishes with an increase in W p. Conversely, in thicker phononic layers, a local maximum in thermal resistance emerges at a specific W p. For smaller thicknesses, the increased overlap in phonon density-of-states between the phononic region and the thermostats at a larger W p , enhances ballistic transport, thereby reducing thermal resistance. In the diffusive limit, the interplay between mode conversion within and between [0 Θ G e ] and [ Θ G e Θ S i ] ranges is pivotal for the observed maximum thermal resistances and distinct temperature profiles in the Si and Ge blocks. Our findings not only highlight differing transport mechanisms at phononic interfaces in ballistic and diffusive regimes, but also demonstrate a novel approach to tuning interfacial thermal resistances using phononic materials. This has significant implications for designing materials optimized for both heat dissipation and energy conversion applications. • Varying the phononic interface parameters lead to a 6-fold ITR change in Si/SiGe/Si • An abnormal maximum of thermal resistance observed at a thick interface region • The maximum ITR arises from mode conversion competition at high and low frequencies • The PDOS overlap between the phononic region and thermostats increases with period [ABSTRACT FROM AUTHOR]

The interface between graphene and natural rubber significantly impacts the thermal properties of graphene/natural rubber composites. This paper uses molecular dynamics to investigate interfacial heat transport. The study found that the thermal conductivity of the composites increases non-linearly with graphene content: a 136 % increase at 10.5 % graphene and only 12.23 % at 16.4 % graphene. As graphene content increases, graphene agglomerates within the natural rubber due to weak van der Waals forces. The interfacial thermal resistance of the composites increases with temperature, rising by 69.94 % from 200K to 450K. When pressure increases from 0.1 MPa to 2.5 MPa, the maximum change in interfacial thermal resistance is 24.39 %. The study also found that interfacial thermal resistance increases with the number of graphene layers. Thus, the interfacial thermal resistance between graphene and natural rubber is the main reason for the minor change in the thermal conductivity of the composites, with temperature having a greater impact. [ABSTRACT FROM AUTHOR]