Maximum Thermal Conductivity Research Articles

Palmitic acid/expanded graphite/CuS composite phase change materials toward efficient thermal storage and photothermal conversion.

In this study, an expanded graphite (EG) with nano-CuS (EG/CuS) support material with a special morphology was prepared, with EG/CuS filled with different ratios of palmitic acid (PA). Finally, a PA/EG/CuS composite phase change thermal storage material with photothermal conversion performance was synthesized. The superb chemical and thermal stability of PA/EG/CuS was demonstrated by characterization and analysis of the experiments. EG, a multi-layer structured material, provides rich binding sites for PA and nano-CuS and constructs rich thermal conductivity paths, which effectively improves the thermal conductivity of PA/EG/CuS. It is noted that the maximum thermal conductivity of PA/EG/CuS reached 0.372 W m-1 K-1 and the maximum phase change thermal storage capacity reached 260.4 kJ kg-1, which proved the excellent thermal storage properties of PA/EG/CuS. In addition, PA/EG/CuS exhibits excellent photothermal conversion performance, and the experimental results demonstrated that the best photothermal conversion efficiency of PA/EG/CuS reached 81.4%. The PA/EG/CuS developed in this study provides a promising method for fabricating excellent conductive and low leakage composite phase change materials for solar energy utilization and energy storage.

Synthesis and Experimental Thermal Adsorption Characteristics of Epoxy Hybrid Composite for Energy Storage Applications

Polymer-based matrix hybrid composites meet their demand in various engineering applications and food industries due to their excellent mechanical, thermal, corrosion, and biodegradable performance. The polymer-based hybrid composites have been a better choice for high thermal insulation at low cost. This experiment attempted to find the thermal adsorption characteristics, heat deflection temperature, linear thermal expansion, and thermal conductivity of epoxy hybrid composites, which contained four different layers of Kevlar and basalt fiber fabricated via a low-cost conventional hand mold layup technique. This experiment revealed that the effect of basalt/Kevlar fiber on epoxy increased thermal performance. The results noted that the hybrid composite consists of less Kevlar fiber with the maximum basalt fiber of sample 4, showed excellent thermal adsorption effect on weight loss limited at 70.98%, and a better heat deflection temperature and[Formula: see text]per °C linear thermal expansion were obtained. Sample 3 exhibited a maximum thermal conductivity of 0.251 W/mK. However, the thermal adsorption of hybrid composite has been limited by more basalt fiber, leading to a 1 wt%/°C decomposition rate.

Experimental investigation on adsorbent composites for CO2 capture application: An attempt to improve the dynamic performance of the parent adsorbent

The present investigation aims at developing consolidated adsorbent composites with enhanced thermophysical and transport properties at the cost of a minimum sacrifice in equilibrium CO2 uptake. Twelve samples are synthesized using a coconut shell-derived activated carbon (CSAC) as the parent material, graphite, graphene nanoplatelets, and CuO as the additives and PVA as the binder. All the synthesized had undergone a proper characterization using N2 adsorption/ desorption and FE-SEM to highlight the changes in the BET surface area, pore volume, pore size distribution, and pore networking compared to the parent activated carbon and surface morphology. The thermophysical (specific heat capacity) and transport properties (thermal conductivity and thermal diffusivity) of all the composites of various mass fractions of the additives (10–40%) are measured using a TPS-2500 S transient hot disk method. The experimental results show that maximum thermal conductivity of 1.72 W/m K is achieved with graphite as the additive with a ratio of CSAC: graphite: PVA (Composite 4) of 50:40:10 wt%, corresponding to an increment of 606% compared to parent CSAC. The increment is comparable and better than the other consolidated adsorbent composites reported in the literature. All the constants of various isotherm models are obtained based on the experimentally obtained pressure-temperature and concentration data using the non-linear regression analysis. Based on the R2 values, the Toth model is identified as the best model for all the composites. A detailed thermodynamic analysis is further carried out, and important thermodynamic parameters, i.e., Enthalpy, Entropy, Gibbs free energy change associated with the adsorption process and the Isosteric heat of adsorption are obtained. The estimated thermodynamic parameters, isotherm and thermophysical data are crucial for the actual design and development of compact systems suitable for adsorption-based CO2 capture applications.

Influence of the different nanostructures of acrylonitrile butadiene styrene/carbon nanotubes nanocomposites on laser cutting properties: Machining and chemical aspects

Reported on in depth for the first time herein is the influence of the diverse nanostructures of acrylonitrile butadiene styrene (ABS)/multi-walled carbon nanotubes (MWCNTs) on its chemical, physical and electrical properties after laser cutting. Injection moulding was used to fabricate the nanocomposite samples in various structures with a thickness of 3 mm by adjusting temperature and pressure. The samples’ nanostructures were evaluated prior to cutting with a CO2 laser. Design of experiments (DoE) by a full-factorial method used three levels laser power 45, 55 and 65 W) and the cutting velocity at three levels (4, 8 and 12 mm/s) as independent variables. The findings from this work are significant and support new theories. It was revealed different surface damage modes such as shrink holes, cracks, decomposed smithereens and sink marks. These were affected by the laser energy density criterion which means that the ratio of power to cutting velocity was the governing factor, whilst the effect of primary nanostructures was negligible. Unlike surface damage, the width of heat affected zone (HAZ) was found to depend on the thermal conductivity, which directly relates to the samples’ nanostructure. Minimum HAZ was obtained at 0.45 mm for the sample with maximum thermal conductivity equal to 0.23 W/mK. Analysis of the post-laser cut surface and HAZ indicated that the MWCNTs were well dispersed with higher orientation and degrees of distribution. This, naturally, allows the inference that application of low laser energy density accounted for and governed oxidation of these regions. The results show that the nanotexture of the post-laser cut surface is completely changed in comparison with the as-moulded surface, leading to the lowest reduction in surface electrical resistivity to 3.2 kΩ for the sample produced at a temperature of 220 °C and a holding pressure of 70 bar.

INFLUENCE OF VARIOUS FACTORS ON THE HEAT TRANSFER CHARACTERISTICS OF MINIATURE TWO-PHASE THERMOSYPHONS WITH NANOFLUIDS

Currently, various types of nanofluids are of increasing interest as heat carriers for heat transfer in thermosiphons and other evaporative-condensation devices. This paper presents and analyzes experimental data on heat transfer characteristics (total thermal resistances, maximum transferable heat fluxes and equivalent thermal conductivity) of two-phase miniature thermosyphons with nanofluids. Geometric parameters of thermosiphons for all experimental samples were identical and were: total length 700 mm, inner diameter 5 mm. The length of the heating zone was changed stepwise from 45 mm to 200 mm. The length of the condensation zone was 200 mm for all investigated thermosyphons. The amount of coolant in the thermosiphons was the same, and its height in the heating zone before the start of the study was 88 mm. Distilled water and aqueous nanofluids with nanoparticles of carbon nanotubes, synthetic diamond, and carbon black were used as heat carriers. The main attention is paid to the study of the influence of the filling factor and the angle of inclination of the thermosyphon, the value of the transferred heat flux and the chemical nature of the coolant (nanofluid) on the heat transfer characteristics of thermosyphons. The strong influence of these factors on the efficiency of a miniature closed two-phase thermosyphon has been demonstrated. A more than twofold increase in the heat transfer characteristics of thermosyphons (the maximal transferred heat flux) was obtained with a sharp decrease in their thermal resistance. It is assumed that the significantly higher heat transfer capacity of such thermosiphons compared to those filled with water is explained not only by the higher thermal conductivity of the coolant, but also by the appearance of a peculiar porous structure that prevents the appearance of a vapor film and promotes the intensification of heat transfer processes during boiling. Bibl. 16, Fig. 10, Tab. 2.

Effects of solar tunnel drying zones and slice thickness on the drying characteristics of taro (Colocasia esculenta (L.) Schott) slice.

This study aims to investigate the effects of slice thicknesses (2, 4, and 6 mm) and solar tunnel drying zones (zone I, zone II, and zone III) on the drying characteristics and thermal properties of taro slices, which were dried using solar tunnel drying (STD). To assess the drying characteristics of taro slices, the data from the drying kinetics were fitted with five different models. The adequacy of fit for the proposed models was evaluated using the reduced chi-square (χ 2), determination of coefficient (R 2), mean relative percent error (P), and root means square error (RMSE). The results showed that, among the five drying models, the drying characteristics of taro are better expressed by the logarithmic model. The thinnest slices dried in zone III had the highest diffusivity (6.57 × 10-09m2/s), lowest specific heat capacity (1.761 kJ/kg °C), and maximum thermal conductivity (0.268 W/m °C). It was also dried within a short period of time (5.5h). The findings of this study provide evidence that STD zones and slice thickness have significant impact on the drying characteristics of dried taro slices.

Effect of Si-coated diamond on the relative density and thermal conductivity of diamond/W composites prepared by SPS

In order to improve the thermal conductivity of tungsten, diamonds coated with thin coating of pure Si and W matrix were mixed to fabricate composites with SPS process. The effects of Si coating and volume fraction of diamonds on microstructure including interfacial structure, relative density and thermal conductivity of the composites were investigated with scanning electron microscopy, X-ray diffraction, transmission electron microscopy and laser thermal conductivity instrument. The results showed that the interface bonding, relative density and thermal conductivity of coated-diamond/W composites were improved compared with uncoated-diamond/W composites under the same volume fraction of diamonds. Increasing in volume fraction of coated diamonds from 30% to 60%, the relative density and thermal conductivity of coated-diamond/W composite increased. Under the combined action of reaction diffusion and inter-diffusion at the interfaces of diamond-Si and diamond-W, the 60 vol% coated-diamond/W composite achieved the maximum thermal conductivity of 193 ± 2.12 W m−1 K−1, which was expected to be used for a longer time than that of W under 20 MW/m2 heat load. Its thermal conductivity was increased with the addition of Si-coated diamond compared with pure W sample (121 ± 1.06 W m−1 K−1) prepared via SPS.

Ultrathin flexible heat pipes with Microsorum fortunei structural-like wick for cooling flexible electronic devices

Ultrathin flexible heat pipes (FHP) with Microsorum fortunei structural-like wicks were fabricated to meet the cooling demands of flexible electronics. The biomimetic wick was fabricated by high-temperature sintering and composed of multi-layer copper mesh and porous micropillars, which corresponded to the veins and spores of Microsorum fortunei leaves, respectively. The aluminum-plastic film was adopted as the casing and endowed the FHPs with insulating capability. FHPs with the thickness of 0.8 mm and 0.67 mm were fabricated by regulating the height of the porous micropillars to form vapor channels with different thicknesses, which reached the maximum thermal conductivity of 1943.5 W/m·K and 1449.5 W/m·K under heating power of 17.1 W and 8.1 W, respectively. The optimum filling ratio was found to be 100% due to its higher thermal conductivity under lower heating powers. FHPs with Microsorum fortunei structural-like wicks achieved good bending heat transfer performances while incurring thermal conductivity fluctuation to within 5.3% under 0–180° bending angles. The infrared tests highlighted that the FHPs maintained good heat transfer performance under natural convection conditions. The advantages of simple manufacture coupled with good bending heat transfer performance and insulating made the FHPs with Microsorum fortunei structural-like wick highly suitable for thermal management of flexible electronics.

Thermal Properties of Graphene based Polymer Nanocomposites

Objective: Epoxy is a commonly used material for electronic components packaging, yet its inherent thermal resistance can’t meet rising demands. To improve the thermal performance of Epoxy material, the high thermal conductivity of Graphene nanoparticles interspersed into the epoxy matrix. This paper focuses on experimental results on the thermal properties of Graphene-based epoxy composite. Methods: Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy used for elemental analysis. Guarded Comparative Longitudinal Heat Flow Technique, thermogravimetric analysis, digital scanning calorimeter, and thermogravimetric analysis used to determine thermal conductivity, Coefficient of thermal expansion, specific heat capacity and thermal stability as per ASTM standard respectively. Findings: Thermal decomposition temperature enhanced from 170 0C of pure epoxy to 329 0C for epoxy with 0.5 wt% of Graphene nanofiller, and it increased with an increase in filler loading, hence proving the thermal stability of composite improved with the addition of graphene nanoparticles. Maximum thermal conductivity of 0.43 W/mK and thermal diffusivity of 0.686 x10-6 m2/s had recorded for 2 wt% of Graphene additives. Linear thermal expansion coefficient and specific heat reduce for the composite material with an increase in filler. Therefore, this indicates heat resistivity improved with minimum heat storage. An increase in stability, conductivity, and diffusivity with the decrease in expansion coefficient and specific heat capacity due to heat proves a favourable factor for thermally conductive material. Novelty: The easy method employed for material preparation, also the use of ultra-low filler content tends to reduce composite cost. Graphene-based Epoxy composites with modified properties represent a conceivable packaging material. Keywords: Thermal Properties; Epoxy composites; Specific heat; Thermal conductivity; Thermal diffusivity

Thermally conductive MWCNTs/Fe3O4/Ti3C2T MXene multi-layer films for broadband electromagnetic interference shielding

• MWCNTs/Fe 3 O 4 /Ti 3 C 2 T x MXene composite film with multi-layer architecture was fabricated by a facile method. • The obtained composite film exhibited high comprehensive performance, including high thermal conduction property and broadband EMI shielding property. • The EMI shielding mechanism of the composite film was comprehensively disclosed. The Ti 3 C 2 T x MXene is thought to be a promising candidate for next-generation electromagnetic interference (EMI) shielding materials. However, its broadband shielding capability and thermal conduction performance are insufficient to meet the growing demands. Herein, we reported a layer-by-layer composite film composed of Ti 3 C 2 T x MXene, multi-walled carbon nanotubes (MWCNTs), and Fe 3 O 4 nanoparticles. Benefitting from the architecture and the synergistic effect of components, the obtained composite film exhibited high comprehensive performance. Specifically, the introduction of Fe 3 O 4 magnetic nanoparticles effectively reduced the impedance mismatch between the composite film and air and enhanced the magnetic loss of the composite film. The layered structure prolonged the transmission path of electromagnetic waves inside the composite film and constructed a rich conductive network, causing interfacial polarization and ohmic loss. The results indicated that the composite film (52 μm) delivered a high EMI shielding effectiveness of 49 dB in the frequency range from X-band to K u -band. Furthermore, the MWCNTs layers in the composite films provided numerous heat transfer channels, reducing phonon scattering during heat transfer and resulting in a maximum thermal conductivity of 8.241 W/(m K).

A novel fractal model for effective thermal conductivity in granular porous media

Quantitative prediction of effective thermal conductivity in porous media is very important in various industrial applications and scientific researches. As the topology and geometry characteristics of pore-solid space is extremely complicated, an accurately theoretical calculation in porous media is still a great challenge. In this study, a novel theoretical model of effective thermal conductivity is derived in granular porous media originated from the Laplace's Equation with a new boundary condition. The proposed model considers the size of solid particles following the fractal distribution characteristics, which is expressed as a function of porosity, fractal dimension of solid particle, maximum particle radius, representative length, and thermal conductivity of both solid particle and pore phase. The predictions of proposed model show a good agreement with the existing models and various published experimental data, which validates its accuracy and reliability. The effect of different geometrical parameters for proposed model is analyzed and discussed. This novel proposed model of effective thermal conductivity may reveal a better insight for thermophysical mechanisms in granular porous media than conventional models.

Direct ink writing of reaction bonded silicon carbide ceramics with high thermal conductivity

Silicon carbide (SiC) ceramic is one of the most used ceramic materials due to its excellent mechanical and thermal properties but the cost is high in production. Three-dimensional (3D) manufacturing of ceramic materials provides the possibility to fabricate ceramic components with unique geometry structures and can save time and cost in producing form and function parts. In this paper, reaction bonded silicon carbide (RBSC) ceramic was fabricated through direct ink writing (DIW) technology. Reaction bonded silicon carbide (RBSC) means infiltration of carbon containing porous green parts with melting silicon, leading to form β-SiC. Remaining pores are filled by residual free silicon. Silicon carbide (SiC) based inks with different carbon black content at solid content of 36 vol% were prepared. The inks consisted of silicon carbide powder as inner filler, carbon black powder and low content sodium alginate as the binder. The effect of carbon black content on rheological behavior was studied. The results showed that the carbon black content played an important role in adjusting the viscosity, modulus and yield point. With the increasing carbon black content, shrinkage of the printed green parts decreased. When the carbon black content reached 20 wt%, the final DIW RBSC ceramics had low residual Si content. The maximum density, flexural strength and thermal conductivity were 2.91 g/cm3, 229 MPa, and 132 W/(m·K), respectively. This study shows a bright prospect of this innovated 3D printing technology for flexibly producing complex and net-shaped RBSC ceramic parts.

Influence of granite powder addition on thermal conductivity of bentonite-based backfill material in ground source heat pump

Granite powder was added to the backfill material of a bentonite-based source heat pump, and the associated effects of granite powder content, dry density, and water content and saturation on thermal conductivity were analyzed. The thermal conductivity improved with increasing water content and dry density, for granite powder contents below 25%. The influence of granite powder on maximum thermal conductivity decreased as water content increased. Thermal conductivity increased with increasing saturation, and it increased faster for saturation below 5%. The results provide a basis for improving the efficiency of ground-source heat pumps and suggest an alternative use for granite powder.

Waste semicoke ash utilized to fabricate shape-stable phase change composites for building heating and cooling

The use of industrial semicoke ash as skeleton material is proposed in this study to fabricate low-cost thermal energy storage materials and shape-stable phase change composites as well as recycle industrial solid waste for building heating. Eight samples with different mass ratios of semicoke ash to NaNO3 are manufactured. Key performance of NaNO3/semi-coke ash shape-stable phase change composite is then investigated using differential scanning calorimetry, laser flash analysis, scanning electron microscopy, X-ray diffraction, and constant-speed pressurization method. Results showed that the sample CC2 with a mass ratio of semicoke ash to NaNO3 of 5:5 demonstrates the absence of visual leakage and deformation and reaches a maximum thermal energy storage capacity of 325.91 J/g in the range of 100 °C to 380 °C, mechanical strength of 96.98 MPa, and maximum thermal conductivity of 1.004 W/(m∙K). In addition, semicoke ash is chemically compatible with NaNO3. Both thermal energy storage capacity and thermal conductivity of sample CC2 increase slightly after 4027 heating/cooling cycles.

Visualization study on operating performance of a dual compensation chamber loop heat pipe under acceleration condition

In this article, a novel visual dual compensation chamber loop heat pipe (DCCLHP) under acceleration conditions was experimentally investigated. The working fluid was deionized water and the wick material was sintered nickel powder. Visual windows were installed on both compensation chambers (CCs) and condenser in order to observe the vapor and liquid distribution. The operating performance and physical mechanism of the proposed DCCLHP under both acceleration direction A and B at different heat loads and acceleration magnitudes were analysed in a systematic manner. Direction A refers the acceleration direction which was parallel to the axis of the evaporator and the CC without a bayonet placed at the outer edge of the rotating arm. While direction B is defined as the acceleration direction was perpendicular to the axis of the evaporator and the evaporator was placed at the outer edge of the rotating arm. In the current study, the heat load varies from 30 W to 130 W and the acceleration magnitude ranges from 1 g to 15 g. Experimental results revealed that: (i) The larger the heat load, the higher the operating temperature. Obviously waving of the vapor-liquid interface in the CC is observed at direction A. Bubbles generated in the CCs and the vapor-liquid interface moves back and forth in the condenser during temperature oscillation at both 70 W and 90 W for the case of 13 g and direction B. (ii) Under direction B, the DCCLHP presents lower operating temperature and higher thermal conductance. The maximum temperature is 143.2 °C at 5 g and 90 W under direction A. The maximum thermal conductance is 1.70 W/K at 13 g and 130 W under direction B. (iii) In general, the operating temperature shows a trend of decreasing first and then increasing with the increase of acceleration. Whereas the thermal conductance shows an opposite behavior. The transition acceleration, namely the acceleration magnitude at the minimum temperature, is 13 g for the case of direction A. However, under direction B, the large heat load can result in a large transition acceleration. (iv) Intermittent spattering of liquid drops is observed in the CCs at 70 W and 15 g under direction A. The flow pattern under direction A is different with that under direction B at each heat load. Multiple segments of the liquid and vapor phase alternately distribute and stratified flow forms in the condenser.

THERMAL PROCESSES IN VITRIFIED TUBES OF A HEAT EXCHANGER

A study was made of the heat maximum transfer coefficients and thermal conductivity of glass coatings of heat exchange tubes. A formula is obtained for determining the optimal value of the thermal conductivity coefficient of a glass coating. It has been established that during long-term operation of the apparatus, the heat transfer coefficient of the glass coating of the pipe practically does not depend on the operating time due to the cleanliness of the glass surface. It has been established that during long-term operation of the apparatus, the heat transfer coefficient of the glass coating of the pipe practically does not depend on the operating time due to the cleanliness of the glass surface. At the same time, in brass or copper pipes, over time, a sharp drop in the heat transfer coefficient occurs due to the formation of a durable layer of scale and corrosion products. For this purpose, a formula has been derived for calculating the value maximum of the heat transfer coefficient of coatings.

Developing Thermal Regulating and Electromagnetic Shielding Nacre-Inspired Graphene-Conjugated Conducting Polymer Film via Apparent Wiedemann-Franz Law.

In this work, we observed size-dependent behavior of filler on both the thermal and electrical conductivities of nacre-like graphene-conjugated conducting polymer films and demonstrated the display of apparent Wiedemann-Franz law and tunability of Lorenz constant in such films. The maximum thermal and electrical conductivities of as-fabricated films can reach over 73 W·m-1·K-1 and 1200 S·cm-1, respectively. Furthermore, the maximum value of electromagnetic interference shielding reaches 54 dB with SSE/t over 16000 dB·cm2·g-1. These films can not only show high-quality electromagnetic interference shielding performance with small thickness and low filler ratio but also achieve simultaneous thermal management during electromagnetic shielding. The findings in this work offer new insight into designing flexible graphene-conjugated polymers with customizable thermal and electrical properties in the broad fields of thermal management systems, electromagnetic defense systems, and flexible electronic systems.

Enhanced High Thermal Conductivity Cellulose Filaments via Hydrodynamic Focusing.

Nanocellulose is regarded as a green and renewable nanomaterial that has attracted increased attention. In this study, we demonstrate that nanocellulose materials can exhibit high thermal conductivity when their nanofibrils are highly aligned and bonded in the form of filaments. The thermal conductivity of individual filaments, consisting of highly aligned cellulose nanofibrils, fabricated by the flow-focusing method is measured in dried condition using a T-type measurement technique. The maximum thermal conductivity of the nanocellulose filaments obtained is 14.5 W/m-K, which is approximately five times higher than those of cellulose nanopaper and cellulose nanocrystals. Structural investigations suggest that the crystallinity of the filament remarkably influence their thermal conductivity. Smaller diameter filaments with higher crystallinity, that is, more internanofibril hydrogen bonds and less intrananofibril disorder, tend to have higher thermal conductivity. Temperature-dependence measurements also reveal that the filaments exhibit phonon transport at effective dimension between 2D and 3D.

Thermal conductivity enhancement of carbon fiber/epoxy composites via constructing three-dimensionally aligned hybrid thermal conductive structures on fiber surfaces

Owing to high graphitization degree, polyacrylonitrile (PAN)-based high modulus carbon fiber (HMCF) can not only be used as the general structural reinforcement for advanced composites, but also be applied to improve the thermal conductivities (TC) of polymer composites. However, the enhancement of through-thickness TC of composites remains extremely challenging due to fiber anisotropy and the lack of continuous thermal conductive path among CFs. In the present work, three-dimensional (3D) hybrid thermal conductive structures were constructed onto PAN-CF surfaces to prepare HMCF/epoxy composites with high through-thickness TC. In details, crosslinked high thermal conductive Ni/CNT hybrid network was firstly electrodeposited onto HMCF surfaces, which also provided abundant channels for the impregnation of easily graphitized poly-p-phenylene benzobisoxazole (PBO)/graphene oxide (GO). The freeze-drying assisted grafting of 3D-oriented PBO/GO and high-temperature heat treatments were further conducted to create the 3D graphite structures onto CFs. The interconnected Ni/CNT networks with 500 nm thickness and 3D aligned PBO-graphite bridging structures with an average thickness of 1 μm contributed to the formation of efficient heat conduction pathways along the through-thickness direction. Additionally, high-temperature treatment had been proven critical to effective heat conductions. Especially, PAN-CF with the 3D hybrid thermal conductive structures treated at 2100 °C (named CNC@PG-2100) exhibited superior TC, and the maximum TC value of CNC@PG-2100 reinforced composites reached 5.39 W/(m‧K) at the CF loading of 55%, which improved by 573% compared to that of composites reinforced by untreated PAN-CFs (0.94 W/(m‧K)).

Preparation of polymer composites with high thermal conductivity by constructing a “double thermal conductive network” via electrostatic spinning

With the advancement of information technology, there is a boom of demand for high-performance thermal conductive polymer-based materials applied in microelectronic devices. Fillers with high thermal conductivity, such as boron nitride nanosheets (BNNS), are often incorporated to improve the comprehensive thermal conductivity of polymer matrix. However, the fillers dispersed in composites often fail to form continuous heat transfer pathways due to the occurrence of interfaces, resulting in a suppressed thermal conductivity. In this paper, BNNS was confined in carbon nanofibers by electrostatic spinning (e-spin). The resultant fibrous carbon-boron nitride hybrid skeleton was combined with silicone rubber to form an elastic composite film. The effects of BNNS contents on the hybrid skeleton morphology and the composite conductivity were rigorously resolved. It was found that the hybrid skeleton consisted of continuous long-stacked carbon fibers, with high thermal conductivity intrinsically. And BNNS was tightly stacked, confined, and oriented along the fibers. The maximum thermal conductivity of the composite film was 4.09 W m−1 K−1, about 16 times higher than that of pure PDMS. A double thermal conductive network mechanism was proposed. That is, the two thermal pathways were formed by the overlapped BNNS and the carbon fibers, respectively. And the optimal thermal conductivity was achieved as the two pathways composited together by spinning and carbonization. The composite films with vertical alignment of the hybrid fibers were also prepared. Our work provides an essential and innovative strategy for the preparation of high thermal conductivity composites.