Interfacial Thermal Resistance Research Articles

Insight into the relationship between interfacial structure and thermal conductivity in epoxy resin/Al2O3 composite

AbstractThe relationship between interfacial structure and thermal conductivity in epoxy resin/Al2O3 composite is important but is still elusive. Here, we illuminate this issue by investigating the role of four silane coupling agents in thermal conductivity for epoxy resin/Al2O3 composites. The results show that 3‐glycidoxypropyltrimethoxysilane (KH560) is the best silane coupling agent to modify Al2O3, resulting in the lowest viscosity and the highest thermal conductivity of the epoxy resin/Al2O3‐KH560 composite compared with alternative systems. This is attributed to the strong interfacial interaction between Al2O3‐KH560 and epoxy resin, as confirmed by the Fowkes model and broadband dielectric spectroscopy. The interfacial thermal resistance between the epoxy resin and Al2O3 is also quantitatively measured via a photothermal radiometry technique. The epoxy resin/Al2O3‐KH560 also has the lowest interfacial thermal resistance (1.50 ± 0.02 × 10−6 m2 K W−1), compared with the other three systems. This study advances the understanding of the relationship between interfacial structure and thermal conductivity in polymer composites.Highlights The relationship between interfacial structure and thermal conductivity in epoxy resin/Al2O3 composite is understood. The interfacial structure is characterized by broadband dielectric spectroscopy. The interfacial thermal resistance is quantitatively measured via a photothermal radiometry technique.

Reducing Kapitza resistance of graphene–paraffin interfaces by alkyl functionalisation

Paraffin waxes are a promising material for heat storage. Improvement of the thermal conductivity can be obtained by adding graphene nanofillers, but interfacial thermal resistance (ITR) forms a problem. Reduction of ITR by functionalisation of the graphene was previously shown possible in the liquid state. For application in heat storage, the thermal properties in solid state are equally important. In the present study, the most optimal reduction of ITR in the solid state was shown for octyl functional groups; in both molten and solid samples, a striking reduction by 95% as compared to pristine graphene was achieved.

Design of Soft/Hard Interface with High Adhesion Energy and Low Interfacial Thermal Resistance via Regulation of Interfacial Hydrogen Bonding Interaction.

Adhesion ability and interfacial thermal transfer capacity at soft/hard interfaces are of critical importance to a wide variety of applications, ranging from electronic packaging and soft electronics to batteries. However, these two properties are difficult to obtain simultaneously due to their conflicting nature at soft/hard interfaces. Herein, we report a polyurethane/silicon interface with both high adhesion energy (13535 J m-2) and low thermal interfacial resistance (0.89 × 10-6 m2 K W-1) by regulating hydrogen interactions at the interface. This is achieved by introducing a soybean-oil-based epoxy cross-linker, which can destroy the hydrogen bonds in polyurethane networks and meanwhile can promote the formation of hydrogen bonds at the polyurethane/silicon interface. This study provides a comprehensive understanding of enhancing adhesion energy and reducing interfacial thermal resistance at soft/hard interfaces, which offers a promising perspective to tailor interfacial properties in various material systems.

Preparations and Thermal Properties of PDMS-AlN-Al2O3 Composites through the Incorporation of Poly(Catechol-Amine)-Modified Boron Nitride Nanotubes

As one of the emerging nanomaterials, boron nitride nanotubes (BNNTs) provide promising opportunities for diverse applications due to their unique properties, such as high thermal conductivity, immense inertness, and high-temperature durability, while the instability of BNNTs due to their high surface induces agglomerates susceptible to the loss of their advantages. Therefore, the proper functionalization of BNNTs is crucial to highlight their fundamental characteristics. Herein, a simplistic low-cost approach of BNNT surface modification through catechol-polyamine (CAPA) interfacial polymerization is postulated to improve its dispersibility on the polymeric matrix. The modified BNNT was assimilated as a filler additive with AlN/Al2O3 filling materials in a PDMS polymeric matrix to prepare a thermal interface material (TIM). The resulting composite exhibits a heightened isotropic thermal conductivity of 8.10 W/mK, which is a ~47.27% increase compared to pristine composite 5.50 W/mK, and this can be ascribed to the improved BNNT dispersion forming interconnected phonon pathways and the thermal interface resistance reduction due to its augmented compatibility with the polymeric matrix. Moreover, the fabricated composite manifests a fire resistance improvement of ~10% in LOI relative to the neat composite sample, which can be correlated to the thermal stability shift in the TGA and DTA data. An enhancement in thermal permanence is stipulated due to a melting point (Tm) shift of ∼38.5 °C upon the integration of BNNT-CAPA. This improvement can be associated with the good distribution and adhesion of BNNT-CAPA in the polymeric matrix, integrated with its inherent thermal stability, good charring capability, and free radical scavenging effect due to the presence of CAPA on its surface. This study offers new insights into BNNT utilization and its corresponding incorporation into the polymeric matrix, which provides a prospective direction in the preparation of multifunctional materials for electric devices.

Enhancing thermal conductance between graphene and epoxy interfaces through non-covalent cation-π interactions

Although graphene has high thermal conductivity, its application in thermal management remains challenging because of the large interfacial thermal resistance between graphene and adjacent materials. This work demonstrates that non-covalent cationic-π interaction can significantly improve the thermal conductance between graphene and substrate interfaces. Cationic polyacrylamide (CPAM) bridges substrate and graphene with hydrogen bonding and cation-π interaction, respectively. The cation-π interaction between graphene and CPAM is confirmed by Raman, UV–Vis and NMR spectroscopy. The results show that CPAM increases the interfacial adhesion of graphene/epoxy from 18.7 ± 2.2 mN to 37.4 ± 7.6 mN (100.0 % improvement) and improves the interfacial thermal conductivity (ITC) from 22 ± 2 MW/m2K to 51 ± 5 MW/m2K (131.8 % improvement). Enhancing the ITC of graphene/epoxy by introducing CPAM assembled layer has advantages over covalent modifications because it provides a similar level of ITC improvement rate, but has little effect on the intrinsic thermal conductivity of graphene. Finally, it is demonstrated that the sample with graphene/cationic polyelectrolyte/substrate structure exhibits great potential for applications in the area of thermal management and printed circuit boards.

High throughput screening of thermal interface materials by machine learning

Till now, it remains a challenge for effective prediction and screening of novel materials with high thermal conductivity, as well as further optimization of the interface thermal resistance. Normally, people have to spend long time on tedious calculations when predicting and screening these materials. In this paper, I combined machine learning with molecular dynamics simulations to investigate the thermal conductive properties of materials with the aim of significantly reducing computational consumption. I first applied molecular dynamics simulations to obtain the relevant properties of materials, then generated models for predicting physical properties by machine learning, and finally made predictions of thermophysical properties of materials. The use of machine learning significantly reduces the prediction time compared to direct molecular dynamics simulations. Especially when the XGBoost and the neural network models are employed, the prediction efficiency is significantly improved. This work guides a new way for the future screening of high-performance thermal interface materials.

Carbon nanotubes grafting aminated epoxy resin with improved elasticity and surface adhesion for enhanced thermal management performance

It is a great challenge to develop thermal interface materials that enable fast heat transfer between the surface of microelectronic materials and heat sinks. In this paper, multi-walled carbon nanotube/epoxy composites (EP-NH2-x) were synthesized by amidation reaction using aminated epoxy resin as matrix and carboxylated multi-walled carbon nanotubes. EP-NH2-x can reduce the interfacial thermal resistance and the promotion of phonon conduction through the chemical bonding connection between the resin and the carbon nanotubes, which will in turn improve the thermal conductivity of the composites. The thermal conductivity of EP-NH2-10 reaches 0.531 W·m−1·K−1 at a and has good variable temperature cycling stability, internal elasticity and surface adhesion. This work highlights the potential application of carbon materials to improve the thermal conductivity of epoxy resins.

A study on novel dual-functional photothermal material for high-efficient solar energy harvesting and storage

The solar-heat storage efficiency of devices based on phase change materials (PCMs) is limited due to the light absorption and internal heat transfer within the PCMs, unclear thermal conductivity-enhancement mechanism within nanocomposite PCMs, and uncontrollable photothermal-interface modulation. Therefore, a novel controllable strategy was proposed in this study to fabricate dual-functional photothermal storage three-dimensional (3D) phase change blocks (PCBs) with higher thermal conductivity (27.98 W/m·K) and spectral absorption (98.03 %) compared to those of most previously reported PCM-based devices. The as-synthesized PCBs contained millimeter-sized graphite plates with horizontal Van der Waals bonds and oriented micro/nanoscale graphite nanosheets. The structural properties of thin PCM layers between the PCB sheets have synergistically reduced the internal interfacial thermal resistance of the PCBs. Laser-controllable induction was used to fabricate integrated biomimetic-forest 3D optical absorbers on the high thermal conductivity interface of the PCBs, which significantly reduced the thermal resistance of the optical-thermal interface. The resulting 3D-PCBs, integrated with thermoelectric generators, powered portable electronic devices, expanding the applications of traditional PCM heat-storage devices. Therefore, this study will guide the future design of high-performance solar-thermal storage PCMs with a wide range of practical applications.

A stabilized state-based peridynamic heat conduction model for interface thermal resistance problems

As the demand for micro/nano-scale electronic devices and composite materials grows, numerical modeling of interfacial thermal resistance problems has become an integral part of the design for these devices and materials. In this work, a stabilized state-based peridynamic heat conduction model considering the Kapitza thermal resistance is proposed. A stabilized scheme is first developed to eliminate the numerical oscillations in the state-based peridynamics. The main idea is to formulate the temperature gradient for each individual bond by penalty function. The corresponding heat flow state is then constructed based on this newly developed bond-augmented temperature gradient in the framework of the Lagrangian formalism. The stabilization scheme is combined with the embedded discontinuous peridynamic concept to capture the temperature jump conditions of interface thermal resistance. The effectiveness of the proposed model is demonstrated by numerical examples. It paves the way for investigating the interfacial thermal resistance problems of materials with complex heat transfer constitutive relations.

Manipulating heat transfer at graphene/silicon interface with nitrogen doping

We perform a numerical evaluation on manipulating the thermal transfer at graphene/silicon by adjusting nitrogen doping modes. The results show that nitrogen doping can reduce the in-plane thermal conductivity of graphene/silicon heterostructure, but when doping is regular and distributed throughout graphene, the thermal conductivity will increase abruptly. This phenomenon can be attributed to the coupling between nitrogen phonons, which provides a new heat transfer channel for in-plane heat transfer. We also detected that the in-plane thermal conductivity of regular doping is higher than that of random doping in all concentration ranges. In the other, we found that nitrogen doping can significantly reduce the interfacial thermal resistance of graphene/silicon interface. The above-mentioned findings provide new ideas and theoretical support for controlling the heat transfer between graphene based heterogeneous interfaces.

Rate-limiting factors in thin-film evaporative heat transfer processes

In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ≫λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O(1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O(1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness of various strategies for exploring the evaporation process in practical thermal management.

Discrete heat equation for a periodic layered system with allowance for the interfacial thermal resistance: General formulation and dispersion analysis.

Discrete heat equations for the multilayered periodic systems with allowance for the thermal resistance between the layers and corresponding dispersion relations in ω-k space have been derived and analyzed. The discrete equations imply a finite velocity of thermal disturbances and guarantee the positiveness of the solutions. Analytical expressions for the attenuation distance, and phase and group velocities have been obtained as functions of frequency and thermal resistance between the discrete layers. These functions demonstrate unusual behavior at high frequency compared to the continuum case. Furthermore, the maximum allowed frequency and wave number for the discrete heat equation are limited, whereas there are no such limits in a continuum. The discrete equation contains an infinite hierarchy of continuous partial differential equations, which starts with the Fourier law, proceeds with the hyperbolic equation, the Guyer-Krumhansl (or Jeffreys type) equation, and then with higher-order equations. The partial differential equations with a finite number of terms are only approximations of the discrete equation, which implies that on the ultrashort space and timescales the discrete approach is preferable. This work provides a relatively simple, easy-to-adopt, conceptual tool, together with analytical expressions allowing one to study ultrafast wavelike heat conduction regimes in periodic multilayered metamaterials.

Thermal Conductivity and Sintering Mechanism of Aluminum/Diamond Composites Prepared by DC-Assisted Fast Hot-Pressing Sintering.

A novel DC-assisted fast hot-pressing (FHP) powder sintering technique was utilized to prepare Al/Diamond composites. Three series of orthogonal experiments were designed and conducted to explore the effects of sintering temperature, sintering pressure, and holding time on the thermal conductivity (TC) and sintering mechanism of an Al-50Diamond composite. Improper sintering temperatures dramatically degraded the TC, as relatively low temperatures (≤520 °C) led to the retention of a large number of pores, while higher temperatures (≥600 °C) caused unavoidable debonding cracks. Excessive pressure (≥100 MPa) induced lattice distortion and the accumulation of dislocations, whereas a prolonged holding time (≥20 min) would most likely cause the Al phase to aggregate into clusters due to surface tension. The optimal process parameters for the preparation of Al-50diamond composites by the FHP method were 560 °C-80 MPa-10 min, corresponding to a density and TC of 3.09 g cm-3 and 527.8 W m-1 K-1, respectively. Structural defects such as pores, dislocations, debonding cracks, and agglomerations within the composite strongly enhance the interfacial thermal resistance (ITR), thereby deteriorating TC performance. Considering the ITR of the binary solid-phase composite, the Hasselman-Johnson model can more accurately predict the TC of Al-50diamond composites for FHP technology under an optimal process with a 3.4% error rate (509.6 W m-1 K-1 to 527.8 W m-1 K-1). The theoretical thermal conductivity of the binary composites estimated by data modeling (Hasselman-Johnson Model, etc.) matches well with the actual thermal conductivity of the sintered samples using the FHP method.

In situ three-roll mill exfoliation approach for fabricating asphalt/graphite nanoplatelet composites as thermal interface materials

Thermal interface materials (TIMs) are vital to dissipate excess heat generated by electronic components with ever-growing power density to ensure their reliability and performance. However, the limited dispersibility of nano-sized thermal conductive fillers hinders further enhancement of thermal conductivity in TIMs. It remains challenging to manufacture high-performance TIMs with simultaneous high thermal conductivity, low cost, and capability of large-scale production. Herein, a solvent-free and scalable approach was adopted to fabricate asphalt/graphite nanoplatelets (GNPs) composites by in situ exfoliating graphite in asphalt melt using a three-roll mill. During exfoliation, asphalt was adsorbed onto the surface of GNPs via π-π interaction and improved their dispersibility. Hence, GNPs formed integrated thermal conductive pathways with reduced interfacial thermal resistance, which significantly improved the thermal conductivity of asphalt/GNP composites. At 25 vol% loading, the asphalt/GNP composite displayed a thermal conductivity of 1.95 W m−1 K−1, showing a 114 % increase compared to the asphalt/commercial GNP (c-GNP) composite prepared by conventional mechanical mixing. Moreover, the heat-resistant and mechanical properties of the asphalt/GNP composites were also enhanced due to the improved filler dispersion and filler-matrix interactions. Thus, the asphalt/GNP composites fabricated by in situ three-roll milling possessed remarkable advantages as TIMs compared with asphalt/c-GNP composites and commercial silicone rubber thermal pads.

Vertically interconnected structure enhances the thermal management capability of copper-based composites

Efficient thermal management relies on constructing a network structure. Here, we propose an efficient strategy for fabricating an in-plane vertically interconnected network by integrating copper nanoparticles and nanowires through electrospinning and vertically stacking hot-pressing. This approach offers a dual benefit: creating an in-plane vertically interconnected thermal conductive network while simultaneously protecting the fillers against oxidation. Furthermore, the combination of multi-dimensional hybrid fillers reduces interfacial thermal resistance. Thus, the (Cu NPs-Cu NWs)@PVP/PVA film with hybrid fillers achieves a high thermal conductivity of 22.71 Wm-1K-1, along with superior thermal stability, oxidation resistance, and flexibility, making it promising for advanced electronic device thermal management.

Silver nanowire bridged graphene framework for encapsulating phase change materials with high thermal conductivity and solar-to-heat conversion ability

To construct a high-efficiency thermally conductive graphene nanoplate (GNP) framework, ball-milling technique and silver nanowires (AgNW) bridging strategy were employed to improve the compatibility of GNP and the interfacial thermal resistance (ITR) in GNP skeletons, respectively. By using unidirectionally freeze casting technique, long range ordered GNP frameworks containing a small amount of AgNW as “bridge” were obtained, which were used to encapsulation phase change material (PCM). As a result, the honeycomb-like micropores of the framework with strong capillary effect give PCM anti-leakage and shape stability. The vertically aligned and AgNW bridged GNP skeletons form high-speed heat transfer paths endowith low ITR, thus significantly improve thermal conductivity to 7.24 W/mK. More importantly, GNP framework with strong light absorption ability endows PCM with well solar-to-heat conversion and storage ability. Therefore, AgNW bridged GNP framework endowing PCM with comprehensive thermal management ability exhibits a high potential in addressing the thermal problems of electronics.

The relation between the atomic mass ratio and quartic anharmonicity in alkali metal hydrides

Phonons play a crucial role in understanding various aspects of solid-state physics, including thermal expansion, phase transition, interfacial thermal resistance, and lattice thermal conductivity (κL). Usually, the three-phonon (3ph) scattering processes have been considered the dominant mechanism governing thermal transport in solids. However, recent studies have revealed that quartic anharmonicity can fill the gap between theoretical calculations based on 3ph interactions and experimental values in a range of materials, such as BAs, perovskite CsPbBr3, and thermoelectric PbTe. Typically, the vibration frequency of phonons is proportional to the inverse square root of the atomic mass. Some semiconductors with heavy atoms have a big mass ratio which leads to a gap between acoustic and optical phonon modes. This phenomenon concurrently suppresses 3ph scattering. The influence of 4ph scattering on κL becomes more important. We investigate the relation between the atomic mass ratio and quartic anharmonicity using rocksalt alkali metal hydrides XH (X = Li, Na, K, Rb, Cs). Our finding reveals a positive correlation between the atomic mass ratio and quartic anharmonicity.

Surface decoration of flexible Si3N4 nanowire membrane by hydroxyapatite micron-flake with excellent thermal insulation at 1300 °C

Flexible and excellent thermal insulation membranes are required as the thermal protection system materials of aerospace vehicles for next-generation space missions. Using ceramic membranes with ultralow thermal conductivity has been proved to be an effective way to protect the electronic components inside the fuselage. Herein, we decorate hydroxyapatite (HA) micron-flake onto Si3N4 nanowire membrane (SR), and investigate the thermal stability, fire-resistance and thermal insulating properties of the obtained SR decorated by HA micron-flake (SRHM). Surface decoration of HA micron-flake onto the SR results in the formation of well-interconnected junctions and the increase of interfacial thermal resistance. Due to the increased interfacial thermal resistance, the as-prepared SRHM exhibits good thermal insulation and outstanding fire-retardant performance. SRHM shows robust mechanical property with tensile strength value of 4.10 MPa, increased by 247.5% compared to the SR without the surface decoration by HA micron-flake. The thermal conductivity of SRHM is as low as 0.037 W m−1 K−1, reduced by 33.9% compared to the SR without the surface decoration by HA micron-flake. After SRHM is heated by a butane blow torch at 1300 °C for 30 min, no obvious change is observed in the macroscopic morphology. And the temperature of the backside for SRHM maintains at a stable temperature of ∼260 °C for 300 s, which is 1040 °C lower than that of the front side. Additionally, SRHM can protect the electronic components form being burnt under the heating of an alcohol lamp for 30 min. The successful preparation of such thermal insulating and fire-retardant SRHM will open up a new world for the widespread applications of ceramic membranes in the fields of aerospace vehicles.

Modelling effective thermal conductivity in polymer composites: A simple cubic structure approach

In this study, we propose the simple cubic model, a distinctive thermal-conductive mathematics for modelling the effective thermal conductivity in polymer composites, taking both filler size and interface thermal resistance into account. This model is constructed by delineating heat transport paths within simple cubic structural units, leveraging principles involving Fourier's law, minimum thermal resistance, specific equivalent thermal conductivity, and thermal resistance network. Demonstrating broad applicability, the simple cubic model accurately predicts effective thermal conductivity within a 0–40 % volume fraction range of filler in polymer composites, maintaining less than 15 % error. Its robustness is validated across over 100 experimental datasets, encompassing various polymer matrices and granular filler types. This extensive validation underscores the model's efficacy, both with our experimental data and existing literature. The simple cubic model's insightful predictions make it valuable in designing and preparing thermally conductive polymer composites.

High‐Performance Bi2Te3‐Based Thermoelectrics Enabled by ≈1 nm Metal Chalcogenide Clusters with Size‐Dependent Electron and Phonon Structures

AbstractThe untapped potential of sub‐nanometric materials (SNMs) in constructing high‐performance thermoelectrics (TE) presents a promising yet unexplored avenue. This study investigates the utilization of supertetrahedral CdS clusters, representing SNMs, in conjunction with state‐of‐the‐art Bi2Te3‐based systems. The CdS cluster with size‐dependent electronic structure enables selective interface scattering of carriers, while its 1 nm size and size‐dependent phonon density of states (DOS) contribute to significant interfacial thermal resistance. Furthermore, interfacial dislocations and significant grain refinement induced by the incorporation of the CdS cluster boost the mechanical properties. Consequently, a remarkable peak figure of merit (ZT) value of 1.47 at 350 K and a record‐high Vickers hardness of 1.08 GPa is achieved in the Bi0.5Sb1.5Te3/0.1 wt% CdS cluster composite. The robust TE module achieves an excellent conversion efficiency of about 6.1% under a ΔT of 241 K. This work opens up exciting possibilities for utilizing 1 nm clusters in thermoelectrics and even inspires other fields involving size‐dependent electrical and thermal transport behaviors.