Low Thermal Resistance Research Articles

Synthesizing SiC layer on diamond by heat treatment and its effects on density and thermal conductivity of diamond/W composite

In order to improve the thermal conductivity of W composites as plasma-facing materials, the interface bonding and interfacial thermal resistance of the composites are the key issues to be solved. Based on our previous study, although Si coating on diamond surface can improve the interface bonding and thermal conductivity of the composite, there still existed the interfacial reaction between W and diamond, which produced more low thermal conductivity compounds (WC/W2C) and added the interfacial thermal resistance of the composites. To further improve the interface bonding and increased the thermal conductivity of diamond/W composites, the Si-coated diamonds were used to prepare the Si-SiC dual layer on diamond via vacuum heat treatment and then to fabricate diamond/W composites (HT-coated diamond/W composite). The effects of temperature and holding time of the heat treatment on coating and its interface bonding with the composites were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that a stable and dense Si-SiC-diamond structure was formed after heat treatment at 1200 °C for 1 h, and the thickness of SiC transition layer was about 20 nm. Thermodynamic analysis demonstrated the reaction rate of SiC increased gradually first and then sharply from 1000 °C to 1400 °C. The integrity of the coating on the diamond surface was strongly impacted by residual compressive stress of the SiC layer, and its value increased with the SiC thickness. The Si-SiC dual layer evidently improved the interface bonding and thermal conductivity of diamond/W composite under the combined influence of reaction diffusion at SiC-W interface, inter-diffusion at W-Si interface, and the orientation relationship at diamond-SiC interface. Theoretical thermal analysis proved that HT-coated diamond/W composite possessing lower interface thermal resistance than that of Si-coated diamond/W composite and raw diamond/W composite achieved higher thermal conductivity of 205 W m−1 K−1.

Covalently Functionalized Leakage-Free Healable Phase Change Interface Materials with Extraordinary High Thermal Conductivity and Low Thermal Resistance.

Phase change material (PCM) has received considerable attention to take advantage of both pad-type and grease-type thermal interface materials (TIMs). However, the fatal drawbacks of leaking, non-recyclability, and low thermal conductivity (κ) hinder industrial applications of PCM TIMs. Herewe report leakage-free healable PCM TIMs with extraordinary high κ and low total thermal resistance (Rt ). The matrix material (OP) is synthesized by covalently functionalizing octadecanol PCM with polyethylene-co-methyl acrylate-co-glycidyl methacrylate polymer through the nucleophilic epoxy ring opening reaction. The OP changes from semi-crystalline to amorphous above the phase transition temperature, preventing leaking. The hydrogen-bond forming functional groups in OP enable nearly perfect healing efficiencies in tensile strength (99.7%), κ (97.0%), and Rt (97.4%). The elaborately designed thermally conductive fillers, silver flakes and multiwalled carbon nanotubes decorated with silver nanoparticles (nAgMWNTs), are additionally introduced in the OP matrix (OP-Ag-nAgMWNT). The nAgMWNTs bridge silver flake islands, resulting in extraordinary high κ (43.4 Wm-1 K-1 ) and low Rt (30.5 mm2 KW-1 ) compared with PCM TIMs in literature. Excellent heat dissipation and recycling demonstration of the OP-Ag-nAgMWNT is also carried out using a computer graphic processing unit. The OP-Ag-nAgMWNT is a promising future TIM for thermal management of mechanical and electrical devices. This article is protected by copyright. All rights reserved.

Thermal characterization of Ge-rich GST/TiN thin multilayers for phase change memories

In the domain of phase change memories (PCMs), intensive research is conducted to reduce the programming cycle cost. The RESET operation is done by melting the PCM and then quenching the liquid phase to put it back to the amorphous state. In most of the devices, the heating is realized by the Joule effect with a titanium nitride (TiN) component put in contact with the PCM itself. One of the crucial points to improve the efficiency of this technology is to characterize the thermal contact between TiN and PCM. Having a low thermal resistance between the heater and the PCM ensures the heat transfer between the two is as efficient as possible. In this work, the interfacial thermal resistance between Ge-doped G2Sb2Te5 (GeGST)/TiN in multilayer systems has been characterized, and the influence of the compressive stress exerted by the TiN layers on the GeGST crystallization has been highlighted.

Effect of GaN/AlGaN Buffer Thickness on the Electrothermal Performance of AlGaN/GaN High Electron Mobility Transistors on Engineered Substrates

AlGaN/GaN high electron mobility transistors on QST engineered substrates are grown with different GaN/AlGaN buffer layer thickness. The as‐grown heterostructures are evaluated for their structural quality via atomic force microscopy, high‐resolution X‐ray diffraction, Raman spectroscopy, and steady‐state thermoreflectance. Transistor devices are fabricated and evaluated via DC and pulsed electrical techniques, as well as thermoreflectance imaging. It is reported that buffer layer thickness of at least 10 μm can result in lateral high electron mobility transistors (HEMTs) with simultaneously high GaN quality, low stress, good DC electrical performance, low current collapse, and low thermal resistance.

Reduction of temperature fluctuation in a South African shack house using phase change material insulation

The majority of South African informal settlements are made from corrugated profile galvanized metal sheets. These informal settlements are prone to temperature fluctuations due to high thermal conductivity of the metal sheet and its low thermal resistance to heat transfer between the exterior and the interior of the shack. Families have resorted to using fuels such as paraffin during cold days, which has resulted in fire outbreaks that ravage surrounding shacks. This study experimentally investigated the temperature fluctuations around a shack fitted with plank chipboard and one without. Energy plus 22.2.0 software was then used to simulate the temperature fluctuations effects after integrating a Phase Change Material (PCM) layer on the shack walls. From the experiments, the internal temperature fluctuations on the shack without the insulations reached close to +50 °C during the day, and −5 °C during the night. While the shack with insulation reached +25 °C during the day and 7 °C during the night. The temperature distribution inside the shack was observed to be uneven, with the top section of the shack at higher temperatures than the bottom section. The region and the location of the shack largely contributed to the temperature fluctuations. Simulations revealed that by integrating a PCM layer in the shack walls, temperature fluctuations were greatly reduced. A lower phase change temperature yielded greater results as the atmospheric air allowed the PCM to fully solidify and melt, thus releasing the latent heat energy. A phase change temperature between 17 and 19 °C was selected based on the average atmospheric yearly temperature range. A 30 mm thick PCM reduced the temperature fluctuations to between +14 °C and +16 °C. However, materials with high thermal conductivity are not well supported by the Conduction Finite Difference used to simulate the performance of a phase change material in energy plus, it is proposed to remove such thin and high conductive materials in the model.

Encapsulation of paraffin-magnetite, paraffin, and polyethylene glycol in concretes as thermal energy storage

These investigations analyze the encapsulation of phase change materials (PCMs): paraffin-magnetite composite, paraffin, and polyethylene glycol (PEG) in concretes. The research aimed to analyze PCMs as a thermal energy storage medium. The concretes were fabricated using the composition of lightweight aggregate, cement, sand, and water. Copper tubes (diameter of 12.7 mm and length of 50 mm) with various formations were installed in the concretes (50 × 50 × 50 mm). The arrangements of the copper tube consist of four-square, four-cross, and six-rectangular tubes. The concretes were then cured for 28 days at an ambient temperature. The copper tubes were filled with the melting paraffin-magnetite composite, paraffin, and PEG. The PCMs analyses include morphology, melting point, latent heat, thermal conductivity, and melting phase transition. The temperature distributions on the concretes filled with the PCMs were monitored using thermocouples and a data logger. The DSC test suggested the highest melting point of 61.65 °C and latent heat of 161.53 J/g obtained in the PEG sample. Adding magnetite particles in paraffin could improve the thermal conductivity to 0.53 W/m·°C compared to paraffin only (0.32 W/m·°C) and PEG (0.28 W/m·°C). The melting phase behavior on the PCMs was affected by the melting point, latent heat, and thermal conductivity. The highest thermal resistance occurred on the concrete where the copper tube only contributes to the low thermal resistance.

Improved wavelength stability and heat dissipation of InGaN-based light-emitting diodes using a graphene interlayer on patterned sapphire substrate

This study presents a straightforward strategy that embeds a graphene interlayer between InGaN-based light-emitting diodes (InGaN LEDs) and patterned sapphire substrate (PSS substrate) for substantial improving device performances of wavelength stability and heat dissipation. The InGaN LEDs on the graphene interlayer/PSS substrate (Gr-LED) have lower piezoelectric fields of 1.16 MV/cm than 1.60 MV/cm for InGaN LEDs on the PSS substrate (Ref-LED). The low piezoelectric field diminishes the screen of the polarization field resulting in a stable electroluminescence peak wavelength. At 100 mA driving current, the chip temperature of Gr-LED shows a decrease in around 24.4 °C relative to Ref-LED. The thermal resistances measured in a vacuum environment are 351 and 128 °C/W for Ref-LED and Gr-LED, respectively. The low thermal resistance of Gr-LED is believed to be due to a low misfit dislocation density of the aluminum nitride nucleation layer that increases the vertical direction of heat transport to PSS. This work demonstrates that the graphene/PSS substrate is a promising substrate for high-power InGaN LEDs.

An overview of the mechanical characterizations and applications of chopped fiber reinforced composites

Composite materials are widely used in many industries due to their basic properties such as high strength, high rigidity, and lightness. However, composites with desired properties differ in each sector. Fiber reinforcement and matrix selection vary depending on application requirements. Composites consisting of reinforcement and matrix elements are classified according to these elements. Chopped fiber reinforced composites, which are included in the classification depending on the reinforcement element, have a wide range of applications. Apart from lightness, it has many advantages, such as high strength, high rigidity, low thermal conductivity, corrosion resistance, and ease of production. Their lower cost of production compared to other composites makes them attractive. It is very important to make various characterizations of these composites in order to improve their properties and expand their use in the places where they are used. Researchers have done many studies on this subject. In this article, a review of the studies is presented. Various mechanical and thermal tests and their results were examined. Different internal structure observations are handled with analysis methods. In addition, the application of chopped fiber reinforced composites is detailed. Suggestions were made for the problems limiting the use of these materials.

Microfluidic silicon interposer for thermal management of GaN device integration

With the popularity of the third generation semiconductor applications, silicon-based hetero-integration is driven to be applied massively by the miniaturization of microsystems and modules. The system-level power has a sharp increase in recent years, and consequently, hotspot thermal management is being increasingly concerned. A high-power GaN device with chip heat fluxes > 500 W/cm2 and hotspot heat fluxes > 30 kW/cm2 is implemented in this work to study extremely uneven hotspot cooling for silicon-based hetero-integration. A customized microjet silicon interposer (SI) is designed and fabricated based on the on-chip hotspot distribution, and another common microchannel SI in similar sizes is prepared for comparison. The GaN device is integrated on SI and micro-assembled in a test cube. The measurement results demonstrate that the maximum junction temperature of the GaN device on microjet SI is down to 150.3 ℃ at 70 ℃ ambient temperature with a pressure drop of 231.9 kPa. The overall thermal resistance (TR) of the test vehicle with microjet cooling has a 7.11 ∼ 7.72 % reduction and its heat transfer coefficient (HTC) increases by 12.3 ∼ 28.3 % compared to that with microchannel cooling with the pumping power of 0.5 ∼ 1.5 W. The material properties of the GaN chip and SI are extracted from the measurement results and then used in the analysis of the thermal and hydraulic properties of both microfluidic SIs numerically. Their cooling performance and efficiency are evaluated and compared based on the performance evaluation criteria (PEC), field synergy number and entropy generation rate. According to the evaluation results, while the PEC of microjet and microchannel SIs increases with the pumping power, the microjet SI can contribute to the enhancement of the synergetic relationship between the flow and temperature fields and reduction of total irreversibility in the heat transfer process compared to the microchannel SI in pursuit of low overall TR. The field synergy number improves by 90.40 % and the argument entropy generation rate is 0.376 when the overall TR is 1.35 K/W. The findings can provide valuable references for hotspot thermal management in silicon-based hetero-integration.

A review on characteristic variation in PLA material with a combination of various nano composites

In search of environmental friendly polymers, poly lactic acid (PLA) emerged as a best alternate to various chemical based polymers. It’s unique characteristics like degradability, eco-friendly, regenerative, easily available, versatile, biocompatibility and having good thermo mechanical properties. At the initial stage of PLA its applications are confined to biomedical sector and within a short period, its applications are widened and used such as packaging materials and especially used where ever the biodegradable properties required. Exhaustion of fossil resources is the world biggest problem, which is the major resource for the process of traditional polymers, in this scenario PLAs are exposed as alternative valuable biopolymer in the field of automation and mechatronics. However, to satisfy the requirements in its wide emerging scope of applications, the pure form of PLAs are facing some drawbacks, as its brittleness, slow rate of degradation, and delicacy, gas permeability, low thermal resistance and rate of crystallization. The negative performance of PLAs can be improved with blending of PLA with other polymers and another way is reinforcement of nanoparticles in to PLA matrix. Economic way of improving the properties is that blending of PLA with other polymers like ABS, Polypropline (PP),Polystyrene(PS) and incorporations of various nano particles such as TiO2, SiO2 etc. This article mainly focuses on the major developments and researches in PLA-based composites during the last decades.

Thermal Performance of Liquid Metal Pastes Containing low Content of Metal Particles for Thermal Interface Materials in IC Module Electronics

In recent years, considerable attention has been paid to gallium-based liquid metal alloys in their use as thermal interface materials for GPU, APU, and HPC in PC and super computers due to its considerably high thermal conductivity and low contact thermal resistance. Gallium-based Liquid metal paste containing low content of metal particles (LMP-MPs) to enhance thermal performance and controllable BLT of the prepared liquid metal composites for thermal interface materials (TIMs) prepared by in-situ introducing gallium oxide into the liquid metal alloys will be reported in our recent research. In this paper, we will report effect of the composition, particle size/types, and bond line thickness on thermal properties of the LMP-MPs. Thermal properties of the LMP-MPs were measured at 50o C using a thermal tester, TIMA5, based on ASTM-D5470 test methodology. It was found in the present study that the composition and types of metal particles, and BLT have significant influence on thermal conductivity, and the conductivity values increase with an increase of the content of metal particles and BLT. However, thermal resistance varies with the change of composition and BLT of LMP-MPs. Scanning electron microscope (SEM) was used to characterize microstructure of LMP-MPs with different metal particles and sizes. Micrographic morphology of the LMPs-MPs shows continuous frame structure observed with SEM, which could keep liquid metals from spreading out and stabilize the phase. We eventually found the LMP-MPs have the better wetting and adhesion properties on bare Cu, glass and bare Si surface than liquid metal alloys that endows good printability to the LMP-MPs. Continuous monitoring of thermal resistance of LMP-MPs at 45o C and 89o C using a house-made thermal tester shows stable thermal resistance after a few months, which indicates LMP-MPs have excellent thermal reliability in ambient atmosphere.

SiC Microchannel Heat Sinks for High Heat Flux Dissipation of 1 kW/cm2

Thermal management has become a major barrier in the development of high-power micro-devices. Microchannel heat sinks (MCHS) are a promising method to dissipate high heat fluxes from high power density devices. Reducing the thermal resistance will reduce the temperature increase of the electronic device, allowing for higher powers to be achieved while maintaining a safe operating temperature. This paper reports on the use of silicon carbide (SiC) microchannels to dissipate high heat fluxes up to 1 kW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over a footprint of 0.25 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The use of high aspect ratio and decreased hydraulic diameter channels has allowed for very low thermal resistances to be achieved at higher heat duties compared to previous studies. The experiments performed resulted in heater temperatures of less than 60 °C and thermal resistances as low as 0.024 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> °C/W between the heater surface and fluid inlet temperature. The demonstrated thermal performance of the SiC MCHS is an encouraging means for dissipating heat from high power density microelectronic devices.

Thermal Synergistic Effect on CFRP Laminates with Modified Fiber/Matrix Systems for Heat Transfer Applications

AbstractCarbon fiber reinforced polymer (CFRP) laminates are modified to enhance their suitability for various thermal applications. A synergistic approach utilizing the effect of various conductive and insulative modifiers with diglycidyl ethers of bisphenol A (DGEBA) epoxy resin and/carbon fiber (CF) is explored. In CFRP laminates developed after modifications made in epoxy resin using a thermoplastic material, such as polycarbonate (PC) and/or acrylonitrile butadiene styrene (ABS), exhibit high thermal resistance (TR) of 77.1% compared to unmodified CFRP. In contrast, modifications made using conductive mediums like phosphonium (P), imidazolium (I), or silanized‐graphene oxide (SGO) have lower TR of 25.7%, 30.5%, and 32.4%, respectively. A temperature gradient (TG) enhancement of 75% is reported for the 1.5 wt% PC/ABS modified CFRP laminates. On the contrary, modifications using 0.5 parts per hundred (phr)P, 0.5 phr I, and 1 g L−1 SGO in epoxy reduce the TG by 25%, 30%, and 32%, respectively. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analyses are done to explore the thermal characteristics of each case of modification. Finally, scanning electron microscopy images confirm the distribution profile of the modifiers used. Based on the types of modifications performed, the current study can offer insightful information on the thermal performances of modified CFRP laminates.

Plasma sprayed ceramic coatings for the thermal protection of carbon fiber reinforced plastics (CFRP): Thermal and mechanical properties of YSZ, aluminum titanate, cordierite and mullite coatings

Carbon fiber reinforced plastic (CFRP) is widely used in lightweight applications because of high values in specific strength and rigidity. However, the use is limited due to a low resistance against wear, low values in hardness and a low thermal resistance. The application of a ceramic TBC can protect the underlying CFRP and thus enhance the temperature resistance when a thermal load is applied.In the present study, Yttria stabilized Zirconia (7YSZ), Aluminum Titanate, Mullite and Cordierite were applied onto CFRP with cyanate ester resin based matrix by atmospheric plasma spraying. Aluminum was used as bond coat material to ensure adequate adhesion of the coatings on the CFRP.Thermal and mechanical properties of the coatings, such as Young's modulus, hardness, porosity, coefficient of thermal expansion, thermal diffusivity and phase composition were measured. The properties of the ceramic coatings were used to evaluate the materials as a potential thermal protection for CFRP substrates. The results show that Cordierite coatings contain a high amount of amorphous phase and have the lowest thermal conductivity as well as the lowest coefficient of thermal expansion among the investigated material systems.

Preparation of Thermally Conductive Silicone Rubber-Based Ultra-Thin Sheets with Low Thermal Resistance and High Mechanical Properties

Thermally conductive silicone rubber (TCSR)-based thin sheets with low thermal resistance and high electrical insulation properties have been widely used in thermal management applications in the electronic and energy storage fields. The low thermal resistance is mainly attributed to the sheets’ small thickness. In order to further decrease the sheets’ thermal resistance, it is necessary to decrease their thickness. However, the sheets mostly have a thickness of at least 0.20 mm, and it is still a challenge to decrease the thickness to less than 0.10 mm mainly due to the difficulty of smooth calendering through a narrow roll-to-roll gap on calenders. Here, a low-viscosity calendering method has been developed to prepare TCSR-based ultra-thin sheets. The sheets present unprecedentedly small thickness (~0.08 mm), low thermal resistance (0.87 cm2K/W), high tensile strength (~8 MPa), high flexibility, high electrical resistance (&gt;1014 Ω·cm), and high thermal dissipation (&gt;30 °C decrease in LED working temperature). Comparison studies between this new method and the conventional preparation method have been carried out to understand the mechanism of the improvements.

Effect of filling ratio, number of loops, and transverse distance on the performance of pulsating heat pipe in a microchannel heat sink

In this study, three-dimensional modeling of a pulsating heat pipe is carried out, and the effect of physical and geometrical parameters such as filling ratio (FR), transverse distance (Z), and the number of loops (N) on its performance is investigated. In this study, it is assumed that the heat pipe is embedded in the microchannel heat sink, and its boundary condition is the thermal condition in the microchannel heat sink. The volume of fluid (VOF) multiphase flow model is used in the current numerical analysis. For the PHP, four different filling ratios (FR = 40, 50, 60, 70%), four transverse distances (Z = 2, 5, 8, 18 mm), and four numbers of loops (N = 1, 2, 3, 4) are considered, and the results will be compared with each other. It is shown that PHP with FR = 60% has the best performance. Also, comparing different values of transverse distance, Z = 18 mm has the lowest thermal resistance. The results show that by embedding a 4-loop PHP, the thermal resistance of MCHS decrease from 0.0268 to 0.0221 K/W, which indicates a 21.27% increase in the thermal performance of the microchannel heat sink compared to the basic design (without PHP).

Performance Assessment of Bioasphalt Mixtures Containing Guayule Resin as an Innovative Biobased Asphalt Alternative

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of 0.65–0.69 kJ/m2 compared to 0.46 kJ/m2 for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, 400 J/m2). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered 591 J/m2 at its performance grade low temperature (−16°C) and 409 J/m2 at −22°C compared to 429 J/m2 for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.

Highly durable, thermally stable, semi-transparent superhydrophobic surfaces for easy-cleaning of contaminants

With the development of smart electronic devices, the importance of surface-protective coatings is rapidly increasing. Superhydrophobic surfaces are promising protective coatings that exhibit potential for anti-wetting, self-cleaning, and antibacterial applications. However, their poor mechanical durability makes their practical application difficult. Additionally, rough surface geometries induce incident light scattering, thereby reducing the transparency and limiting their optical applications. This study describes semi-transparent superhydrophobic surfaces with improved mechanical strength and thermal stability obtained through simple spray coating. We mixed reactive polydimethylsiloxane (PDMS) as a binder with low surface free energy and high thermal resistance with fluorinated silica nanoparticles. PDMS polymers were functionalized to improve their hydrophobicity and adhesion properties through hydrosilylation with acrylate monomers. As a result, our superhydrophobic surfaces had a high-water repellency of above 160° and transparency of approximately 60 % at a wavelength of 550 nm. The coated surfaces exhibited an outstanding pencil hardness of 5H and sufficient clarity to identify objects through them. After heat treatment at 400 °C, the hardness increased to 6H while maintaining superhydrophobicity. Additionally, various contaminants were easily removed with water spraying. Our semi-transparent superhydrophobic surfaces can be widely applied in hard coatings for mobile displays, solar cell panels, self-cleaning paint, and outdoor facilities.

Thermal assessment of a new planar thermal diode integrated collector storage solar water heater in different partial vacuums: An experimental study

Thermal diodes are novel mechanisms with high thermal resistance in one direction and low thermal resistance in the other. The current study introduces a new planar thermal diode integrated collector storage (ICSs) system and analyzes its transient dynamics and performance under field conditions in several scenarios, including operating at atmospheric pressure and partial vacuums: Ptotal = 0.7 atm and 0.5 atm. The acquired data illustrate that the collector has approximately the same transient dynamics during the collection period, while differences pronounce during the retention period. Utilizing partial vacuums is tricky and may cause to decrease in performance; however, the best retention and collection efficiencies were obtained at 16.97% and 29.33% when Ptotal = 0.7 atm was utilized. Increasing the partial vacuums to Ptotal = 0.5 atm decreases the retention efficiency significantly to nearly 3.26%. The heat gain (forward mode) coefficient was not affected significantly by partial vacuums. However, the heat loss (reverse mode) coefficient was reduced by nearly 17.63% at Ptotal = 0.7 atm compared to atmospheric pressure. The calculated heat gain and heat loss coefficients are 9.28 W/k and 19.65 W/k at Ptotal = 0.7 atm; hence, the constructed thermal diode successfully serves as a unidirectional heat transfer mechanism.

Improvement of Heat Resistance of Fluorosilicone Rubber Employing Vinyl-Functionalized POSS as a Chemical Crosslinking Agent.

Fluorosilicone rubber (F-LSR) is a promising material that can be applied in various cutting-edge industries. However, the slightly lower thermal resistance of F-LSR compared with that of conventional PDMS is difficult to overcome by applying nonreactive conventional fillers that readily agglomerate owing to their incompatible structure. Polyhedral oligomeric silsesquioxane with vinyl groups (POSS-V) is a suitable material that may satisfy this requirement. Herein, F-LSR-POSS was prepared using POSS-V as a chemical crosslinking agent chemically bonded with F-LSR through hydrosilylation. All F-LSR-POSSs were successfully prepared and most of the POSS-Vs were uniformly dispersed in the F-LSR-POSSs, as confirmed by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H-NMR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements. The mechanical strength and crosslinking density of the F-LSR-POSSs were determined using a universal testing machine (UTM) and dynamic mechanical analysis (DMA), respectively. Finally, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements confirmed that the low-temperature thermal properties were maintained, and the heat resistance was significantly improved compared with conventional F-LSR. Eventually, the poor heat resistance of the F-LSR was overcome with three-dimensional high-density crosslinking by introducing POSS-V as a chemical crosslinking agent, thereby expanding the potential fluorosilicone applications.