Maximum Thermal Conductivity Research Articles

Find the maximum thermal conductivity of graphene reinforced polymer composite: A molecular dynamics approach

AbstractThe ultrahigh in‐plane thermal conductivity makes the graphene nanoplatelet a promising reinforcement filler for improving the thermal conductivity of polymer materials. Up to now, the highest thermal conductivity enhancement has been achieved by aligning the nanoplatelets along the heat flux direction. In this work, extensive molecular dynamics simulations are carried out to understand the thermal conductivity enhancement capabilities of different architectures of the graphene nanoplatelets within the polyamide‐6 matrix. Surprisingly, we find that the orthogonally arranged graphene nanoplatelets offer even better thermal conductivity enhancement than the simply aligned graphene nanoplatelets. An in‐depth investigation shows that the orthogonal structure can achieve a balance between the global percolation and the alignment of graphene nanoplatelets. Specifically, such an orthogonal structure can take advantage of both thermal percolation and graphene's ultrahigh in‐plane thermal conductivity. Moreover, we have systematically investigated the effects of the size and number density of the nanoplatelets on the thermal conductivity enhancement capability of the orthogonal configuration. Finally, by proposing a validated analytical model, we have identified the pathways to maximize the thermal conductivity of the orthogonally arranged graphene nanoplatelets. The conclusion of this work points out the possible way to develop the graphene‐polymer composite system with exceedingly high thermal conductivity.Highlights Different graphene configurations are constructed for polymer composite. Chemical reactions at the edge of graphene nanoplatelets are considered. High‐throughput molecular dynamics simulations are conducted to measure thermal conductivity. Competition between graphene alignment and thermal percolation is identified. A theoretical model is established for graphene‐polymer composite.

Why is the thermal conductivity of Janus nanofluid larger? – From the perspective of aggregation morphology

The nanoparticle aggregation is a crucial factor for the thermal conductivity of nanofluids based on previous researches. Molecular dynamics simulations for the nanofluids involving 4–32 Janus nanoparticles (termed as Janus nanofluid) were conducted. The thermal conductivity of the Janus nanofluid was found to be larger than that of the ordinary nanofluid, approximately 0.3707 W/m.K for Janus, compared to 0.3521 W/m.K for Au and 0.3303 W/m.K for Cu nanofluid. Further analysis shows that the aggregation morphology in the Janus nanofluid is different from that in the ordinary one. For the better evaluation of the aggregation morphology, a term named degree of looseness was introduced to replace fractal dimension. The relationship between thermal conductivity and degree of looseness shows that the thermal conductivity of the Janus nanofluid first rises and then decreases with the degree of looseness. When 18 nanoparticles are included in the simulated system, the maximum thermal conductivity is 0.3249 W/m.K for a moderate degree of looseness of 10.841 at 4 vol%. Finally, the underlying mechanism why the Janus nanofluid has a larger thermal conductivity than the ordinary one is discussed. This can provide a useful reference for preparing Janus nanofluids with larger thermal conductivity and understanding the underlying mechanisms.

Twist-Dependent Anisotropic Thermal Conductivity in Homogeneous MoS2 Stacks

Thermal transport property of homogeneous twisted molybdenum disulfide (MoS2) is investigated using non-equilibrium molecular dynamics simulations with the state-of-art force fields. The simulation results demonstrate that the cross-plane thermal conductivity strongly depends on the interfacial twist angle, while it has only a minor effect on the in-plane thermal conductivity, exhibiting a highly anisotropic nature. A frequency-decomposed phonon analysis showed that the cross-plane and in-plane thermal conductivity of MoS2 are dominated by the phonons with frequencies below 12.5 THz and 7.5 THz, respectively. As the interfacial twist angle increases, these low-frequency phonons significantly attenuate the phonon transport across the interface, leading to impeded cross-plane thermal transport. However, the in-plane phonon transport is almost unaffected, which allows for maintaining high in-plane thermal conductivity. Furthermore, our study revealed a strong size dependence for both cross-plane and in-plane thermal conductivities due to the influence of low-frequency phonons in MoS2. The maximum thermal conductivity anisotropy ratio is estimated as ∼400 for twisted MoS2 from our simulation, which is in the same order of magnitude as recent experimental results (∼900). Our study highlights the potential of twist engineering as a tool for tailoring the thermal transport properties of layered materials.

Pressure-induced tuning of thermal transport in carbon-based composites: Directional control of heat dissipation

Aggressive miniaturization in the electronics industry demands more efficient thermal management for electronic devices. Employing the excluded volume approach, we enhanced thermal conductivity (TC) and manipulated heat dissipation in a polymer composite loaded with a thermally conductive filler—graphene nanoplatelets (GNP)—alone or supplemented with a high-volume filler (diamonds). This yielded a maximum bulk TC of 4.5 W m−1K−1 (no compression). The heat dissipation direction could be controlled by compressing (≥50 bars) the wet composite before curing, resulting in an enhancement of the cross-plane thermal conductivity (for thermal-interface materials) to 12.3 W m−1K−1. For non-compressed samples, in-plane thermal conductivity (for circuit board conformal coatings) was dominant (8 Wm−1K−1). Our holistic approach meets diverse thermal management needs.

Aramid nanofiber based Ag/Fe3O4-CNT/rGO hybrid membrane for high-performance electromagnetic interference shielding

With the increase of modern integrated electronic and telecommunication systems, high-performance electromagnetic interference (EMI) shielding materials with flexibility, outstanding thermal conductive properties and superior EMI shielding performances are designed to solve the problems of electromagnetic radiation and heat accumulation. Herein, flexible asymmetric trilaminar architecture film with good mechanical properties is prepared via the facile three-step vacuum-assisted filtration (VAF) followed by hot-pressing approach, which is composed of silver-plated aramid nanofibers (ANF-Ag), ANF-Fe3O4&CNT (ANF-FC) and ANF-reduced graphene oxide (ANF-rGO) layers. The conductive ANF-Ag and ANF-rGO layers acted as the EMI shielding, thermal conductive layers, and supporting substrate layers. The magnetic ANF-FC layer played the important role in synergistically enhancing the EMI shielding performance. The resultant flexible and asymmetric trilaminar hybrid membrane with a thickness of 112 µm exhibited maximum thermal conductivity of 8.5 W m−1 K−1 and EMI SE of 67.5 dB, but also maintained a high tensile strength of 75.5 MPa and superb electrical conductivity of 2.46 × 106 S/m. This asymmetric trilaminar structures film holds great promise to addresses issues of electromagnetic radiation and heat accumulation for personal smart electronic devices, wearable electronics, electronic telecommunication systems.

Thermal, mechanical, and photocatalytic dye degradation performances of the functionalized GO and TiO2 decorated carbon foam composites

Although pitch-derived carbon foam (CF) is not new, but the progress for enhanced thermal, mechanical, and catalytic dye degradations need to be explored. Numerous works were performed to improve the structural morphology and properties of the CFs by dispersing various additives. But mostly it was noticed that such additives enhanced one aspect of the CFs at the cost of other ones. In this work, various additive loadings of the functionalized graphene oxide (FGO), and functionalized titanium dioxide (FTiO2) were synergistically dispersed into the CF matrix via facile pyrolysis for the preparation of CF/FGO and CF/FGO + FTiO2 hybrid composites to improve the structural morphology and properties of the CFs. Functionalization of the graphene oxide (GO) and titanium dioxide (TiO2) nanoparticles (NPs) was performed for the purpose to decrease the possible aggregations, and enhancing the compatibility and interaction between the additives and the CF matrix. A total of seven CF composites including pure CF were synthesized and explored for their structural, thermal, mechanical, and catalytic dye degradation performances. The microstructural investigations revealed that cellular morphology, pore size, shape, and porous homogeneity of the CF composites were significantly improved after the FGO and FTiO2 loadings. The thermal and mechanical behaviors revealed that as the additives loading of the FGO and FTiO2 are increased, the thermal and mechanical responses of the CF composites are significantly improved. The maximum thermal conductivity of 27.9 W/m K was revealed by 4wt.% CF/FGO + FTiO2 hybrid composite. Similarly, the optimum compressive strength of 15.7 MPa, specific compressive strength of 3.5 10 m3, excellent stress–strain, and improved Young's modulus of 42.2 MPa was shown by 4wt.% FGO + FTiO2 hybrid composite. The catalytic activity was evaluated by degrading orange II dye in an aqueous medium under ultraviolet (UV) light irradiation. The TiO2-containing composite was found to be active and the sample with 4wt.% CF/FGO + FTiO2 hybrid composite achieved a significant 78.9% degradation of the dye within just 80 min.

A systematic molecular dynamics study of the thermal conductivities of polyetherimide/graphene nanocomposites using response surface methodology

AbstractIn this work, an I‐optimal response surface model was used to systematically investigate the effects of graphene (Gr) content (Factor A; 0–10 wt%), temperature (Factor B; 0–200°C), and Gr layer structure (Factor C; monolayer versus five‐layer) on the thermal conductivities of PEI/Gr nanocomposites, which were determined using reverse non‐equilibrium molecular dynamics (RNEMD) simulation with the Müller‐Plathe algorithm. Based on a reduced quadratic model that was fit to the data, the effect of Factor A on thermal conductivity was found to be more pronounced for the PEI/Gr nanocomposite with the five‐layer Gr structure. Moreover, Factor B had expectedly the largest effect on thermal conductivity, followed by Factor C. However, these two factors were involved in significant interactions with Factor A. Based on numerical optimizations, the predicted thermal conductivities of the PEI/Gr nanocomposites varied from 0.057 (minimum) to 0.174 W m−1 K−1 (maximum). Overall, the maximum thermal conductivity of the PEI/Gr nanocomposite may be obtained at any given temperature in the range of 0–200°C by the addition of multi‐layer Gr (a cheaper alternative to monolayer Gr) at a content of 10 wt%. For example, the addition of 10 wt% five‐layer Gr to PEI at room temperature (25°) results yields an increase in its thermal conductivity of about 30%. Also, going from 0 to 100°C, an increase of about 76% is predicted for the thermal conductivity of the PEI/Gr nanocomposite containing 10 wt% five‐layer Gr. The results of this study shed light on the interactions between the three investigated factors.Highlights Thermal conductivities of polyetherimide/graphene (PEI/Gr) nanocomposites simulated. Graphene (Gr) content, temperature, and Gr layer structure affected the thermal behavior. Response surface methodology (RSM) aided in the identification of factorial interactions. Numerical optimization of the thermal conductivities enabled by a predictive model.

Enhanced thermal conductivity in Ag-H2O nanofluids by nanoparticles of different shapes: Insights from molecular dynamics simulation

The mechanism of thermal conductivity enhancements and influential factors make a lot of sense in the intensive investigation of nanofluids. While numerous studies have explored the effect of solid–liquid interfacial layers on thermal conductivity improvement in water-based nanofluids with diverse applications, investigations into the intrinsic mechanisms underlying interfacial layers in relation to nanoparticle shape remain limited. The thermal conductivity of water-based Ag-H2O nanofluids was investigated using molecular dynamics simulations of non-equilibrium molecular dynamics (NEMD), with emphasis placed on the shape and volume fraction of nanoparticles. The influence of nanofluid volume fraction on thermal conductivity was revealed through visual analysis of 3D smoothed surface plots, highlighting the positive correlation between thermal properties and increasing volume fraction of nanoparticles. Moreover, the contribution of different shapes of silver nanoparticles to thermal conductivity enhancement demonstrated an increasing trend with the corresponding growth in surface-to-volume ratio (S/V values associated with different particle shapes). For the volume fraction of 1.5%, the minimum thermal conductivity enhancement of 22.75% was observed for the spherical shape, while the maximum thermal conductivity enhancement of 25.51% was achieved with the triple-platelet particles. Importantly, the comprehensive analysis of radial distribution function (RDF) and mean square displacement (MSD) indicated the positive effect of interfacial nanolayers influenced by nanoparticles of various shapes on the thermal conductivity of nanofluids. This study provides valuable insights into the impact of nanoparticle shape on the thermal properties of nanofluids, opening up promising prospects for future molecular dynamics simulations.

Effective modulation of lattice thermal conductivity in monolayer AlP3 by biaxial strain and external electric field

Tunable lattice thermal conductivity is a critical issue promoting thermoelectric performance of potential thermoelectric materials. Herein, the effects of biaxial strain and an external electric field on the lattice thermal conductivity of monolayer AlP3 have been investigated systematically by solving the phonon Boltzmann transport equation based on first-principles calculations. Our results imply that the lattice thermal conductivity of monolayer AlP3 can be effectively modulated in a wide range depending on the applied in-plane biaxial tensile strains or out-of-plane external electric fields. Once the biaxial tensile strain is applied to the monolayer, the lattice thermal conductivity exhibits an up-and-down behavior with an increase in the tensile strain. The maximum thermal conductivity is obtained at a tensile strain of 6%, and a surprising peak value of 13.8 times higher than that of the pristine monolayer can be achieved, whereas the lattice thermal conductivity of monolayer AlP3 is able to be further suppressed by applying an external electric field, and a minimum value of about 47.5% of the pristine one can be observed by utilizing an electric field of 0.06 eV/Å. Thus, this work highlights that biaxial strain combined with an external electric field can provide effective ways to realize robust thermal management for 2D triphosphides.

Thermal conductivity prediction of WO3-CuO-Ag (35:40:25)/water hybrid ternary nanofluid with Artificial Neural Network and back-propagation algorithm

One way to enhance the thermal conduction process in heating systems is to attach substances with high thermal conductivity (TC) to the base fluids. The interesting properties of NF (nanofluids) and the significant capability for growing TC have caused this group of fluids to be of great interest to researchers in recent years. Hence, in this study, the thermal conductivity of WO3-CuO-Ag (35:40:25) /water nanofluid (NF) with affected Artificial Neural Network (ANN) and back-propagation algorithm is investigated and predicted. The objective of this research is to develop a sophisticated data analysis model that can evaluate intricate relationships that impact the thermal conductivity of HNF in terms of temperature and solid volume fraction (SVF). This study is performed at 6 temperatures (T) of 25, 30, 35, 40, 45, and 50 °C and 4 vol fractions (φ) of 1%, 0.2%, 0.3%, and 0.4%. The regression plot for the datasets a remarkable resemblance to unity, indicating a robust correlation between the predicted values from ANN and the actual values. Notably, the predicted values in ANN are indistinguishable from 0.998, indicating a near equivalence between the projected and actual values. The results show that increasing the φ of NP and T has led to a rise in the TC of studied NF, and at a high-T level, the maximum TC value is reached when the φ is extended to the maximum value. Also, the results indicate that T sensitivity plays a more significant role than φ in increasing the TC of WO3-CuO-Ag (35:40:25) /water NF. The maximum and minimum values of the sensitivity analysis for T equal 177.4501–431.489098 in five ANNs, and φ equals 16.2539901–37.2332646, respectively. Eight neurons are the best number in the hidden layer (HL) based on different trained ANNs.

Super-thick highly thermally conductive graphite/Sn laminated composites assembled by active Ti-containing Sn-Ag-Ti filler metals

The development of highly performance thermal management material becomes critical in recent years due to the high integration of electronic products. In order to prolong the thickness of graphite materials, we propose a new process to fabricate thick graphite/Sn laminated composites based on brazing technology. The active filler metal was added to form solid combination between thin highly thermally conductive graphite films. The achieved laminated composites have maximum thickness of 4.375 mm and maximum thermal conductivity of 983 W/m·K. Furthermore, the thicker laminated composites could be obtained by using this method as well. The composites are proved to possess high heat flux during process of heat transfer, and the transfer rate was almost twice that of traditional thermal conductivity metal such as Cu and Al. Copper used 74 s to raise 15 °C, while 60-layer composites only took 37 s in the same level under equivalent experimental condition. The maximum 64.21 MPa tensile strength was obtained. The elongation gradually rises with the growth thickness of the composites. 18.9 % elongation was achieved with 20-layer composites. With the controllable thickness and reliable mechanical properties, the composites are able to be a solution for heat dissipation of integrated appliances.

Effect of Working Fluid, Orientation, and Cooling Mode on Thermal Performance of Miniature Flat Heat Pipe

Abstract Flat heat pipes (FHPs) are commonly used as a passive cooling system in portable electronic gadgets due to their compact profile. The present study investigates the effect of different working fluids on the thermal performance of a miniature FHP under different orientations and condenser cooling mechanisms and the start-up performance of FHP. Deionized water, acetone, ethanol, and methanol are chosen as working fluids in the FHP. Five different inclinations (0 deg (horizontal), 30 deg, 45 deg, 60 deg, and 90 deg (vertical)) and two different condenser cooling methods (natural convection and forced convection with fan cooling) are considered in this experimental study. The FHP thermal performance is quantified in terms of overall temperature difference, thermal resistance, and effective thermal conductivity. The results indicate that comparatively higher effective thermal conductivity values are obtained for methanol and acetone heat pipes at low heat loads and under natural convection. At higher heat loads, the ethanol heat pipe had higher effective thermal conductivity values for the same condenser cooling method. For the case of the forced convection cooling mode, the methanol heat pipe had enhanced thermal performance as compared to the other three fluids for all heat load ranges and different inclinations. Due to the higher boiling point of water, as a working fluid water is not suitable in most of the experimental trials except at high heat load under forced convection cooling and in a horizontal orientation. The maximum effective thermal conductivity of 7846 W/mK is obtained for FHP filled with methanol at 24 W heat load and 90 deg orientation under forced convection condenser cooling.

Synergistic effects of oriented AlN skeletons and 1D SiC nanowires for enhancing the thermal conductivity of epoxy composites

As electronic devices are moving towards miniaturization and integration, the demand for ceramic/polymer composites with high thermal conductivity (TC) are increasing significantly. Herein, we reported a novel idea for rational design and delicate construction of anisotropic three-dimensional thermally conductive networks via the ice template method, using stearic acid-modified AlN particles (AlNm) as the primary filler and SiC nanowires (SiCNWs) as the secondary. As predicted, the as-prepared epoxy (EP)-based composites achieved a maximum TC of 2.56 W·m−1·K−1 in vertical direction at a filling fraction of 55 vol %, which was 12.8 times higher than that of pure EP. More importantly, the enhancement mechanism of composite TC was further demonstrated by realistic heat transfer process and finite element simulations. Furthermore, the prepared composites also displayed excellent thermal stability, high mechanical strength and good dielectric property, indicating that this strategy provides a promising insight for the design of high-performance thermal interface materials (TIMs).

Achieving high-temperature thermal evacuation between dissimilar materials Cf/C and Mo30Cu by forming a brazed joint

Achieving a high heat transfer is essential for the Cf/C-Mo30Cu dissimilar material components in their applications of thermal nuclear reactions. In this study, the Cf/C composite and the Mo30Cu alloy were successfully brazed by using the Ag-Cu-4.5Ti braze to eliminate interface gaps between them. The maximum thermal conductivity of the Cf/C-Mo30Cu joint at 860 °C /10 min reached 112 W·m−1·K−1(RT). The thermal conductivity of the joint even exceeds that of the Cf/C matrix (107 W·m−1·K−1). It is worth noting that the overall thermal conductivity of the joint can still reach 92 W·m−1·K−1 at 500 °C. Shear test results showed that the average shear strength of the joints achieved 13.1 MPa at the highest thermal conductivity of the joint. A homogeneous TiC layer is generated along the Cf/C interface, which is crucial for maintaining a stable joint and providing a favorable heat transfer channel across the Cf/C-Mo30Cu dissimilar materials.

Experimental comparison and numerical study of flow and heat transfer characteristics of the pipe rows in heat pipe heat exchanger

Lube oil cooling is a very important heat transfer process on board, and the use of liquid-liquid heat pipe heat exchangers (HPHE) is easier to maintain and save energy, and does not have the risk of leakage. In this work, the heat transfer and flow in the heat pipe row of liquid-liquid HPHE is analyzed. The numerical model of HPHE based on the thermal resistance network of heat pipe is constructed and verified with the actual experimental data, and its maximum deviation is 8.1%. Results show that increasing the working fluid temperature in the evaporative section improved the operating performance of the heat pipe inside the HPHE, with the maximum equivalent thermal conductivity reaching 7112 W·m−1·K−1 at 70 °C. Furthermore, increasing the hot fluid flow rate improved the heat transfer rate of the HPHE more than increasing the cold fluid inlet flow rate. The convective heat transfer performance equations were fitted to the HPHE, with reliable accuracy within 5% obtained for both the forced convection correlations in the condensing and evaporating sections. The pipe row effect was observed to have some variability, with the periodic variation of the heat transfer coefficient per pipe row being more pronounced. The heat transfer coefficient of the pipe row at the outlet decreased by 15.5%, and the heat transfer coefficient of the pipe row at the baffle gap was also about 15% lower than that of the middle pipe row.

Microstructure evolution of Si3N4 ceramics with high thermal conductivity by using Y2O3 and MgSiN2 as sintering additives

Silicon nitride (Si3N4) ceramics were prepared by gas-pressure sintering using Y2O3–MgSiN2 as a sintering additive. The densification behavior, phase transition, and microstructure evolution were investigated in detail, and the relevance between the microstructure and the performance (including thermal conductivity and mechanical properties) was further discussed. A significant change from a bimodal to a homogeneous microstructure and a decreased grain size occurred with increasing Y2O3–MgSiN2 content. When the small quantity of preformed β-Si3N4 nuclei grew preferentially and rapidly in a short time, an obvious bimodal microstructure was obtained in the sample with 4 mol% and 6 mol% Y2O3–MgSiN2. When more β-Si3N4 nuclei grew at a relatively rapid rate, the sample with 8 mol% Y2O3–MgSiN2 showed a microstructure consisting of numerous abnormally grown β-Si3N4 grains and small grains. When more β-Si3N4 nuclei grew simultaneously and slowly, there was a homogeneous microstructure and smaller grains in the sample containing 10 mol% Y2O3–MgSiN2. Benefitting from the completely dense, significant bimodal microstructure, low grain boundary phase, and excellent Si3N4–Si3N4 contiguity, the sample containing 6 mol% Y2O3–MgSiN2 exhibited great comprehensive performance, with a maximum thermal conductivity and fracture toughness of 84.1 W/(m⋅K) and 8.97 MPa m1/2, as well as a flexural strength of 880.2 MPa.

Structural, Mechanical and Thermal Properties of Cement Effect of Fractional Addition of Rice Husk Ash

It has been established that Rice Husk Ash (RHA) contains a large amount of Silica and causes environmental problems if left to burn. An inevitable and preliminary interest of the current work was to investigate the effect of partial replacement of RHA in ordinary Portland cement (OPC) regarding variation in its compressive strength, thermal conductivity and structural properties. The RHA was obtained via controlled burning followed by grinding and replacement with OPC. RHA has been added at various percentages from 10 to 50% with an incremental step size of 10%. The properties of the final product have been investigated after preservation of the samples for 3, 7, 14, 21, 28, 56, and 90 days. The study reveals that samples containing 10% of RHA exhibit maximum compressive strength of 2066.33 Psi with a density of 2.65g/cm3 when cured for 28 days. Due to high relative humidity and temperature after 28 days the strength was slightly lower than the specimen preserved in water. The thermal conductivity measurements revealed that samples with 50% of RHA exhibit minimum thermal conductivity as 0.81 Btu/ft2/hr/0F while maximum thermal conductivity was obtained at 10% RHA replacement. XRD analysis showed a significant transformation in the phase and crystallinity of the mixture. The average crystallite size of pure RHA was 2227.69 Å, however, for the mixture, the crystallite size was observed to be 712.2 and 162.77 Å with 10 and 40 % of the RHA, respectively. This study concluded that partial replacement of RHA in OPC provides a low-cost and insulating building material for the construction industry.

Experimental study on the effect of graphene and Al2O3 nanofluids in a miniature flat heat pipe

The miniature flat heat pipe (mFHP) is a promising cooling technique for the thermal control of portable electronic appliances. The thermal behavior of miniature flat heat pipe (mFHP) with graphene-DI water and Al2O3-DI water-based nanofluid is experimentally investigated. The copper-made mFHP has dimensions of 200 mm in length, 10 mm in breadth, and 3 mm in thickness. The effect of nanofluid, tilt angle (0˚, 30˚, 45˚, 60˚ and 90˚), condenser cooling mode (natural convection and forced convection with fan cooling), and heat load on the effective thermal conductivity of mFHP are analyzed in this present work. The results reveal that the mFHP filled with nanofluid as working fluids shows better thermal performance as compared to those with the base fluid alone. The FHP filled with Al2O3-DI water nanofluid achieves the maximum effective thermal conductivity of 6271 W/mK under a heat load of 14 W and 60˚ orientation with natural convection condenser cooling. A heat pipe's wettability and capillary pressure are both enhanced by using nanofluid as the working fluid. As the optimum orientation of mFHP varies based on the combined effect of the type of nanofluid used in FHP, the heat load range, and the method of condenser cooling; hence it is very difficult to obtain its value analytically. Therefore, the experimental findings help in selecting the design parameters of mFHP for suitable applications.

Simultaneously Improved Thermal Conductivity and Dielectric Properties of NBR Composites by Constructing 3D Hybrid Filler Networks

AbstractThis work aims to address the heat accumulation issue in electronic components during high‐frequency operation through the preparation of novel thermally conductive composites. First, polydopamine (PDA) and in‐situ growth of silver (Ag) nanoparticles are applied for the surface modification of graphene oxide (GO) and carbon nanotube (CNT) to prepare pGO@Ag and pCNT@Ag hybrid filler, respectively. Then, nitrile butadiene rubber (NBR) is chosen as the polymeric matrix and simultaneously incorporated with both pGO@Ag and pCNT@Ag to prepare polymeric composites with excellent thermal conductivity (TC) and dielectric constant (ɛr). Due to the construction of 3D heat conduction networks by utilizing 2D pGO@Ag and 1D pCNT@Ag, the fabricated NBR composites achieved the maximum TC of 1.0112 W/(mK), which is 636% higher than that of neat NBR (0.1373 W (mK)−1). At the filler loading of 9 vol%, the TC of pGO@Ag/pCNT@Ag/NBR composite is 152% that of GO/CNT/NBR composite (0.6660 W (mK)−1). Moreover, due to electron polarization effect of GO and CNT and micro‐capacitor effect of Ag nanoparticles, a large ɛr of 147.12 is attained at 10 Hz for NBR composites. Overall, the development of dielectric polymer materials with high TC is beneficial for enhancing the service life and safety stability of the electronic components.

Thermal Response of Biocarbon-Filled Hemp Fiber-Reinforced Bioepoxy Composites.

We investigated the thermal conductivity of materials based on pyrolysis temperature, filler loading, filler size, and type of biomass feedstock. Hemp stalk and switchgrass were pyrolyzed at 450, 550, and 650 °C and crushed into 50, 75, and 100 μm particle sizes. Biocarbon fillers (10, 15, and 20 wt %) were added to the bioepoxy polymer matrix. The study showed increased filler loading and particle size increased thermal conductivity-the biocomposite samples with 20 wt % filler loading of 100 μm particle size of the biocarbon obtained at 650 °C showed the maximum thermal conductivity in both hemp biocarbon-filled composites (0.59 W·m-1·K-1) and switchgrass-filled composites (0.58 W·m-1·K-1) with the highest flame time. Biocarbon in biofiber-reinforced polymer composites can improve thermal conductivity and extend the flame time. These findings significantly contribute to developing hemp-based bioepoxy composite materials for thermal applications in various fields. These include insulating materials for buildings and thermal management systems, energy-efficient applications, and help in material selection and product design with a positive environmental impact.