High Thermal Reliability Research Articles

Form-Stable Phase-Change Materials Using Chemical Vapor Deposition-Derived Porous Supports: Carbon Nanotube/Diatomite Hybrid Powder and Carbon Nanotube Sponges

In this work, two types of chemical vapor deposition (CVD)-derived porous supporting materials consisting of CNTs–decorated diatomite (CNT/DE) and CNT sponges (CNS) were developed to prepare novel form-stable phase-change material (PCM) composites by impregnation, using polyethylene glycol (PEG) as the PCM. The CNT/DE support matrix showed highly entangled nanotubes (the weight ratio of CNTs to DE was 0.16) over and inside the porous structure of diatomite, giving the hybrid matrix an electrical response. The CNS that resulted was mainly composed of bent and interconnected CNTs forming a three-dimensional highly porous structure. XPS and FTIR results revealed that CNTs in both the supporting materials have a moderate amount of oxygen-containing functional groups. Both hosts allow for high PEG loading (about 75 wt%) without showing any PCM leakage during melting. Both form-stable PCM composites showed high thermal reliability upon a hundred melting–solidification DSC cycles (PEG/CNT/DE latent heat is 86 ± 4 J/g and PEG/CNS latent heat is 100 ± 2 J/g; melting temperature 34 °C). An analytical model was used to evaluate the passive cooling performance of the systems, simulating the thermal behaviour of a building wall containing the confined PCM in the hosts, resulting in a reduction in required cooling power of about 10%. The overall results suggest that the developed form-stable PCM composites could be considered promising additive materials for the production of building envelopes with thermal energy storage capability.

Integrating MXene Film With Recyclable Polyethylene Glycol-co-Polyphosphazene Copolymer as Solid-Solid Phase Change Material for Versatile Applications.

Phase-change materials (PCMs) stand a pivotal advancement in thermal energy storage and management due to their reversible phase transitions to store and release an abundance of heat energy. However, conventional solid-liquid PCMs suffer from fluidity and leakage in their molten state, limiting their applications at advanced levels. Herein, a novel Zn2+-crosslinked polyethylene glycol-co-polyphosphazene copolymer (PCEPN-Zn) as a solid-solid PCM through dynamic metal-ligand coordination is first designed and synthesized. The as-synthesized PCEPN-Zn is further integrated with an MXene film to construct a double-layered phase-change composite through layer-by layer adhesion. Owing to the introduction of MXene film with low emissivity, good light absorptivity, and nonflammability, the resultant phase-change composite not only presents a high latent-heat capacity, good thermal stability, high thermal reliability, and excellent shape stability, but also exhibits a superior self-healing ability, good recyclability, high adhesivity, and good flame-retardant performance. It can be easily adhered to on most objects for various application scenarios. With a combination of the excellent functions derived from PCEPN-Zn and MXene film, the developed phase-change composite exhibits broad prospects for versatile applications in the thermal management of CPUs and Li-ion batteries, thermal infrared stealth of high-temperature objects, heat therapy in the clinic, and fire-safety for various scenarios.

Preparation and thermal stability research of oxalic acid dihydrate-glutaric acid/PAMPS phase change gel for solar thermal energy utilization

Thermal energy storage technology based on phase change materials (PCMs) can address the temporal and spatial mismatches in solar thermal energy conversion, thereby enhancing solar energy utilization efficiency. However, the liquid flow and poor thermal reliability of PCMs limit their large-scale application in solar thermal systems. In this study, we employ a simple “one-pot method” to prepare a form-stable and thermally reliable oxalic acid dihydrate-glutaric acid/poly 2-Acrylamido-2-methyl-1-propanesulfonic acid (OAD-GA/PAMPS) phase change gel. The OAD-GA/PAMPS phase change gel melts at 64.5 °C with a phase change enthalpy of 193.6 kJ/kg, the tensile strength is 7.707 MPa, and the compressive strength is 16.940 MPa. By incorporating 5 wt% BN particles, the thermal conductivity of OAD-GA/PAMPS phase change gel reaches 0.63 W/(m·K). After 200 heating-cooling cycles, the phase change temperature of the OAD-GA/PAMPS phase change gel remains nearly unchanged, and the phase change enthalpy decreases by only 5.7 %. The photo-thermal conversion efficiency of the OAD-GA/PAMPS phase change gel is 82.7 %. The high thermal reliability and photo-thermal conversion efficiency of the OAD-GA/PAMPS phase change gel makes it suitable for solar thermal energy storage applications.

A novel stearic acid/expanded graphite/Fe3O4 composite phase change material with effective photo/electro/magneto-triggered thermal conversion and storage for thermotherapy applications

Composite phase change materials (CPCMs) have demonstrated high potential in thermotherapy; however, their poor energy conversion limits thermal−charge performance, thus negatively affecting their practical applications. Herein, we combined stearic acid (SA), expanded graphite (EG), and Fe3O4 nanoparticles (NPs) to obtain an 80 wt% SA/EG/Fe3O4 CPCM with multisource−triggered thermal conversion and storage abilities. The CPCM was equipped with a photothermal conversion facilitated by high light absorption of EG and localized surface plasmon resonance of Fe3O4. The high electrical conductivity of EG also offered the CPCM with an effective electrothermal conversion. An accelerated magnetothermal conversion was further achieved for the CPCM owing to the superparamagnetism of Fe3O4 NPs. Resultantly, the 80 wt% SA/EG/Fe3O4 CPCM could be facily charged as applied with either low−energy electricity (2.0 V), actual sunlight radiation (98−110 mW/cm2), or alternating magnetic field (120 W). In addition, it exhibited relatively high thermal storage capacity (152.4 J/g), excellent leakage resistance, and high thermal stability, conductivity, and cycling reliability. As in the form of a heat pack, the 80 wt% SA/EG/Fe3O4 CPCM maintained a heat release to a human back within 50–52 °C for 34 min, overtaking the criteria for high−temperature thermotherapy. The proposed multisource−triggered thermal conversion abilities and suitable thermal properties made SA/EG/Fe3O4 CPCM promising for multiple energy utilization and practical thermotherapy applications.

Study on Thermal Cycling Reliability of Epoxy-Enhanced SAC305 Solder Joint.

In this work, epoxy was added into commercial Sn-3.0Ag-0.5Cu (SAC305) solder paste to enhance the thermal cycling reliability of the joint. The microstructure and fracture surface were observed using a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and a shear test was performed on the thermally cycled joint samples. The results indicated that during the thermal cycling test, the epoxy protective layer on the surface of the epoxy-enhanced SAC305 solder joint could significantly alleviate the thermal stress caused by coefficients of thermal expansion (CTE) mismatch, resulting in fewer structural defects. The interfacial compound of the original SAC305 solder joints gradually coarsened due to the accelerated atomic diffusion, but epoxy-enhanced SAC305 solder joints demonstrated a thinner interfacial layer and a smaller IMC grain size. Due to the reduced stress concentration and the additional mechanical support provided by the cured epoxy layer, epoxy-enhanced SAC305 solder joints displayed superior shear performance compared to the original joint during the thermal cycling test. After 1000 thermal cycles, Cu-Sn IMC regions were observed on the fracture surfaces of the original SAC305 solder joint, exhibiting brittle fracture characteristics. However, the fracture of the SAC305 solder joint with 8 wt.% epoxy remained within the solder bulk and exhibited a ductile fracture mode. This work indicates that epoxy-enhanced SAC305 solder pastes display high thermal cycling reliability and could meet the design needs of advanced packaging technology for high-performance electronic packaging materials.

Isotropic negative thermal expansion in the multiple-phase La-Fe-Co-Si alloys with enhanced strength and ductility

The negative thermal expansion materials based on the magneto-volume transition are usually poor in mechanical properties, severely inhibiting their application. Here in this article, we present the enforcement of the compressive strength and ductility of La(Fe,Co,Si)13 by directly adding extra Cu element and forming natural multiple phases alloys. Our study demonstrates that the extra Cu will facilitate the formation of LaCu2 phase that is semi-coherent with the La(Fe,Co,Si)13 phase, and the LaCuSi phase that exhibits a high density of stacking faults, which facilitates the enforcement of the strength and ductility of the alloy. Consequently, the natural alloys present increased strength from 70 MPa to 645 MPa, and the deformation behavior transforms from brittle to plastic, the ductility is simultaneously increased from 0.5 % to 4.4 %. The introduced phases exhibit positive thermal expansion behavior and compensate for the negative thermal expansion of the La(Fe,Co,Si)13 phase, inducing a tunable isotropic negative to zero thermal expansion is achieved in the alloys. Moreover, the alloys have high mechanical and negative thermal expansion performance reliability after 104 times thermal cycles. This work denotes that Cu is a functional element to enforce the mechanical properties of the La(Fe,Co,Si)13 alloys, and also promotes a new possibility for obtaining low-cost and isotropic negative/zero thermal expansion materials with high application reliability.

Low-temperature co-fired ceramics with high thermal expansion and reliability for millimeter-wave antennas

Low-temperature co-fired ceramics with high thermal expansion and reliability for millimeter-wave antennas

Effect of Grain Structure of Gold Plating Layer on Environmental Reliability of Sintered Ag-Au Joints.

Gold-plated substrate is widely used in sintering with silver paste because of its high conductivity, stability, and corrosion resistance. However, due to massive interdiffusion between Ag and Au atoms, it is challenging for sintered Ag-Au joints to maintain high reliability. In order to study the effect of grain structure of gold plating layer on the environmental reliability of sintered Ag-Au joints, we prepared four substrates with different gold structures. In addition to the original gold structure (Au substrate), other gold structures were obtained by heat treatment at temperatures of 150 °C (Au-150 substrate), 250 °C (Au-250 substrate), and 350 °C (Au-350 substrate) for 1 h. Compared with the other three gold substrates, the sinter jointed on the Au-350 substrate obtained the highest shear strength. By analyzing the grain structure of the gold plating layer, it is found that the average grain size of the Au-350 substrate is the largest, and the proportion of low-angle grain boundaries is less. Few grain boundaries have a positive impact on inhibiting the excessive diffusion of Ag atoms and improving the bonding performance of the joint. Based on the above study, we further evaluated the environmental reliability of sintered joints. In 150 °C high-thermal storage, the interdiffusion of Ag and Au in the sintered joint on the Au-350 substrate was restricted, retaining stronger bonding until 200 h. In a hygrothermal environment of 85 °C/85% RH, the shear strength of the sintered Ag-Au joint with the Au-350 substrate maintained above 40.2 MPa during 100 h aging. The results indicated that the sintered Ag-Au joint on the Au-350 substrate with the largest grain size has superior high thermal reliability and hygrothermal reliability.

Studies on 8.4 W/m·K thermally conductive silicone rubber with high compressibility, high electrical insulation, high thermal reliability, and low cost

Thermally conductive silicone rubber (TCSR) has been widely used to enhance heat dissipation in electronics and energy storage devices. Currently, it is a challenge to produce TCSR which combines high thermal conductivity, high compressibility, high thermal reliability, high electrical insulation, and low cost. Here, we report a state-of-the-art TCSR which achieves such a combination. Owing to the optimized alumina gradation, the loading level of alumina in the TCSR reaches 96 wt%. The TCSR reaches a high and isotropic thermal conductivity of 8.4 W/m·K, a high compression ratio of 48 % (under a pressure of 6 psi or 42.4 kPa), and a high dielectric strength (>6 kV/mm). After heating at 180 °C for 100 h, little oil bleeding is observed. More importantly, these properties remain stable (variation < 10 %) after 2000 h of thermal aging at 135 °C, indicating high thermal reliability.

Polydopamine based silver coated cenosphere microcapsule for thermal energy storage

In the present work, low-cost and eco-friendly metallic multi-shell wall microcapsules having paraffin wax were synthesized by encapsulating them with industrial waste cenosphere. Acid etching of the cenosphere shell wall was carried out to create multiple pores through which liquefied paraffin was vacuum infiltrated. Later, metallic coating of Ag was done through surface functionalizing the microcapsule with bio-polymer polydopamine (PD). The metallic coating is adapted to provide a dual function in terms of sealing the pores as well as increasing the thermal conductivity of the microcapsules. Further, the coating also provides additional mechanical strength of the microcapsule. Scanning electron microscopy (SEM) images showed that the mean diameter of the cenospheres was ∼67 µm and the pore diameter was ∼2 µm. The thickness of the Ag coating was ∼773 nm. The Fourier transform infrared (FTIR) Spectroscopy and X-ray photoelectron spectroscopy (XPS) results of the functionalized microcapsules showed additional peaks attributing to functional groups introduced after PD polymerization. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) results inferred that the thermal storage capacity of the microcapsule was 99.92% with high thermal reliability. Furthermore, silver coated microcapsules showed ∼33% enhanced heat transfer performance than uncoated microcapsules as evidenced by TT-curve. The metallic coating at the outer shell and PCM at the inner core of the cenosphere enable it to be a potential thermal energy storage (TES) material for versatile engineering applications.

Low Loss/Low CTE Semiconductor Carrier Packaging Thin Core Material

There is an ever-increasing need by semiconductor/packaging companies for the introduction of a low loss, ultra-low Coefficient of Thermal Expansion chip carrier packaging substrate core material that provides a cost-effective method for producing thin core build up with very dense core vias. This low loss, low CTE flip-chip substrate core is well suited to multi-layer, RF, and applications requiring a system-in-package approach. This paper discusses a novel substrate core material using a build-up film dielectric layer in conjunction with glass fiber weave. Key properties include low loss (Df&lt;0.002), a CTE from 5 - 10 ppm/C, extremely high thermal reliability, and low modulus. An advantage of using glass fiber weave instead of Invar, for instance, is the extremely low CTE that can be achieved while still maintaining a non-conductive power or ground plane. Multilayer circuits using PTFE can suffer from extremely high lamination temperatures, high cost, and low overall yields due to the inability of the soft material to go through a desmear process. Substrate core materials have the primary benefit that they offer stability and increased reliability of many subsequent build-up microvia layers. As monolithic semiconductors are replaced by chiplets, there is a growing need to package many types of chiplets without losing the signal integrity performance of a monolithic semiconductor on a single IC package. An extremely low loss substrate core offers the potential benefit that unique chiplet packaging architectures can be designed with the lowest possible dielectric losses due to the multichip interconnect strategy.

Effect of the cross-linking of polyorganosiloxane on highly thermally conductive silicone rubber's mechanical, dielectric, and thermally conductive properties and thermal reliability

With the rapid development of thermal management techniques, there is an urgent need for thermally conductive silicone rubber (TCSR) which has high softness, high electrical insulation, high thermal conductivity, and high reliability. Currently, the reliability problem has received little attention in the academic reports. Herein, the effect of the cross-linking of polyorganosiloxane on TCSR's mechanical, dielectric, and thermal properties and thermal reliability has been studied. It is found that the cross-linking has great impacts on the thermal reliability of mechanical and oil bleeding properties, and slight impacts on the thermal reliability of dielectric and thermally conductive properties. When the content of hydrogen-terminated silicone oil is 2–4 phr and the content of hydrogen-side silicone oil is 1.5–1.8 phr, the resultant TCSR has high properties, including high softness (Shore OO hardness 55−68), high compression ratio (20−40 % @ 20 psi), high dielectric strength (5.3−5.7 kV/mm), high thermal conductivity (4.3−4.8 W/mK), and high thermal reliability (less than 10 % variation for most properties after thermal aging). Possible mechanisms have been discussed.

Design of Sustainable Self‐Healing Phase Change Materials by Dynamic Semi‐Interpenetrating Network Structure

AbstractThe design of sustainable self‐healing phase change materials (SHPCMs) remains challenging depending on sustainable fatty alcohols without compromising high enthalpy efficiency. Herein, the semi‐interpenetrating network (semi‐IPN)‐based SHPCMs are developed by introducing dynamic disulfide crosslinking polyurethane networks and sustainable fatty alcohols as phase change components in a semi‐IPN structure, enabling the combination of ultrahigh enthalpy efficiency of ≈100% and excellent self‐healing ability with 99% of mechanical stain healing efficiency. The latent heat (61.6–144.3 J g−1) and phase change temperature (29.2–64.2 °C) can be readily adjusted by the type and content of fatty alcohols in SHPCMs. The SHPCMs present high thermal reliability, thermal and shape stability, and solid‐like rheological properties benefiting from the advantage of the semi‐IPN structure. The SHPCMs are endowed with tunable mechanical stress (1.23–6.16 MPa) and strain (5.77–379.48%). More importantly, the SHPCMs can be nearly completely self‐healed after thermal stimulus, complying with the Arrhenius model, with a low activation energy of 33.831 kJ mol−1. This innovative strategy opens new avenues for preparing efficient and durable thermal energy storage materials with high enthalpy efficiency, self‐healing ability, and sustainable phase change components, broadening their potential applications.

Preparation and thermophysical properties of a novel metallic microencapsulated phase change material/eutectic salt/ceramic composite

The development of thermal storage material is crucial for the utilization of thermal energy. At present, eutectic salt/ceramic composite has been widely studied as latent heat storage material, however, its thermal conductivity is low and its latent heat per unit volume is still not ideal, despite its high latent heat per unit mass. Herein, a metallic microcapsule with high thermal conductivity and latent heat per unit volume is introduced to improve the above properties. Using MgO as the support material, metallic microcapsule (Sn@Void@SiO2) and eutectic salt (LiNO3-NaCl) with almost the same temperature range as phase change material, metallic microcapsule/eutectic salt/ceramic composite was prepared by cold-pressure sintering method. The result shows that the best performance of metallic microcapsule/eutectic salt/ceramic composite was achieved with the addition of 30 wt% Sn@Void@SiO2 instead of MgO, the latent heat per unit volume and per unit mass of the composite are 237.1 J/cm3 and 117.9 J/g, which are improved by 56.72 % and 15.48 % respectively. And the thermal conductivity of the composite was improved by 63.79 %, from 0.58 W/(m·K) to 0.95 W/(m·K). Further, the addition of a small amount of Sn to metallic microcapsule/eutectic salt/ceramic composite can not only increase its latent heat but also improve its thermal conductivity as Sn fills the pores inside the composite after melting. The result showed that the thermal conductivity of the composite was increased by 155.17 % than that of eutectic salt/ceramic composite when Sn was added at 5 wt%. Finally, thermal cycle results showed that composites have high thermal reliability and proved high thermal cycling stability of metallic microcapsule prepared by “double-layer coating, sacrificial inner layer” method.

Intrinsic Flame Retardancy and Flexible Solid-Solid Phase Change Materials with Self-Healing and Recyclability.

Conventional polymeric phase change materials (PCMs) have been widely used due to their high heat storage density, small temperature variation, and nontoxicity. However, the high flammability and unrecyclable problems restrict their applications in energy storage devices (ESDs). Although it is facile to introduce a flame retardant into phase change materials to improve fire resistance, the physical blending will deteriorate the mechanical performance and thermal stability of PCMs. Herein, flame-retardant solid-solid PCMs (FRPCMs) with intrinsic flame retardancy, phase change property, self-healing, and recyclability were synthesized by simultaneously integrating tetrabromobisphenol A (TBBPA) and poly(ethylene glycol) (PEG) into polyurethane network skeletons. PEG ingredients acted as phase change materials, and TBBPA not only worked as an efficient flame retardant but also provided dynamic covalent bonds for thermally induced self-healing and recyclability. FRPCMs possess the highest latent heat of 124.7 J/g, high self-healing ability, and high thermal reliability and recyclability. Besides, with the introduction of TBBPA, the limiting oxygen index (LOI) value and char residue significantly increased, the heat release rate (HRR) and total heat release (THR) values decreased, and most of the FRPCMs reached UL94 V-2 rating as well. Hence, the synthesized FRPCMs could expand the application scope of PCMs for thermal energy storage.

Flexible highly thermally conductive biphasic composite films for multifunctional solar/electro-thermal conversion energy storage and thermal management

Phase change materials (PCMs) have been widely used for thermal energy storage in overcoming the intermittence of renewable energy and passive thermal management. However, low thermal conductivity, leakage, inherent brittleness, and lack of responses under multiple stimuli preclude their widespread applications. Here, we report a flexible and form-stable solid-solid/solid-liquid biphasic phase change composites to achieve efficient solar/electro-thermal energy conversion and storage as well as thermal management of high-power devices simultaneously. Proposed biphasic polyurethane–stearic acid/expanded graphite (PU–SA/EG) composites demonstrate state-of-the-art performances with a high energy storage density of 117.4–137.3 J/g and high thermal conductivity of 10.98–37.80 W/(m⋅K) simultaneously at an EG loading ratio of 10–30 wt %, benefiting from the formation of continuous thermal transport network provided by expanded graphite nanosheets. PU–SA/EG maintains high flexibility and good thermal reliability over more than 500 melting/solidification cycles. High solar- and electro-thermal conversion and storage efficiencies of up to 90.5% and 88.7% are achieved, respectively. When applied in thermal management of flexible electronic devices, PU–SA/EG film demonstrates a superior cooling performance by reducing device temperature prominently by 32 °C under a DC 5A discharging power supply. This work provides an effective way for harvesting and storing multiple energy sources like solar energy and electricity, as well as thermal management of high-power electronic devices.

Polyurethane/n-Octadecane Phase-Change Microcapsules via Emulsion Interfacial Polymerization: The Effect of Paraffin Loading on Capsule Shell Formation and Latent Heat Storage Properties.

Organic phase-change materials (PCMs) hold promise in developing advanced thermoregulation and responsive energy systems owing to their high latent heat capacity and thermal reliability. However, organic PCMs are prone to leakages in the liquid state and, thus, are hardly applicable in their pristine form. Herein, we encapsulated organic PCM n-Octadecane into polyurethane capsules via polymerization of commercially available polymethylene polyphenylene isocyanate and polyethylene glycol at the interface oil-in-water emulsion and studied how various n-Octadecane feeding affected the shell formation, capsule structure, and latent heat storage properties. The successful shell polymerization and encapsulation of n-Octadecane dissolved in the oil core was verified by confocal microscopy and Fourier-transform infrared spectroscopy. The mean capsule size varied from 9.4 to 16.7 µm while the shell was found to reduce in thickness from 460 to 220 nm as the n-Octadecane feeding increased. Conversely, the latent heat storage capacity increased from 50 to 132 J/g corresponding to the growth in actual n-Octadecane content from 25% to 67% as revealed by differential scanning calorimetry. The actual n-Octadecane content increased non-linearly along with the n-Octadecane feeding and reached a plateau at 66-67% corresponded to 3.44-3.69 core-to-monomer ratio. Finally, the capsules with the reasonable combination of structural and thermal properties were evaluated as a thermoregulating additive to a commercially available paint.

Thermal performance enhancement of high durability alloy microencapsulated phase change material (MEPCM)/ceramic composites based on industrial graphene

Metallic phase change material (PCM)/ceramic composites have emerged as promising candidates for medium and high-temperature thermal energy storage (TES) due to their excellent performance. However, challenges associated with leakage and oxidation in metals, along with the limited thermal conductivity of ceramic matrices, restrict further performance enhancement. Herein, an alloy microencapsulated phase change material (MEPCM) is prepared as a PCM using the “double-layer coating, sacrificial inner layer” method, followed by compounding it with a ceramic matrix and industrial graphene (IG). Based on this, a novel IG/SnBi58 MEPCM/ceramic composite is prepared and its performances are investigated. The results show that the composite with 12 wt% IG exhibits optimum performance: a thermal conductivity of 5.75 W/(m·K), 86.1% higher than without IG, melting enthalpy of 73.71 J/cm3, and compressive strength of 49.38 MPa. Furthermore, the microencapsulation of alloys fundamentally solves the PCM leakage issue within the composite and enables its good component compatibility. The heat storage density reaches 399.1 MJ/m3, over 2.3 times that of traditional quartz sensible heat storage materials. Owing to the thermally expanded cavities created by “double-layer coating, sacrificial inner layer” method, the prepared MEPCM demonstrates high thermal reliability, so the composite maintains stable thermal properties and chemical structure after 500 thermal cycles. Finally, the comparative analysis reveals that the composite combines higher thermal conductivity, compressive strength, heat storage density, and thermal cycle stability than other composite heat storage materials. This work provides a new strategy to meet the demand for high-performance heat storage materials in medium-temperature TES applications.

Hierarchical thermal-conductive polymer nanocomposites for thermal management

Managing heat in electrical conductors is a major challenge to meet the demands for sustainable energy use and electrical reliability, most notably power electronics and energy-critical electrical machines. Achieving such disparate functionalities, such as high temperature thermal and electrical reliability, require rational design and manufacturing of thermal conductor material and its hierarchical structures. Here we present hierarchical thermal-conductive nanocomposites, consisting of nanostructured ceramic conformal coating and aligned ultrahigh molecular weight polyethylene fiber, to tailor heat dissipation in electric conductors. The hybrid aligned thermal interface exhibits a highly desirable temperature dependent anisotropic high thermal conductivity with 0.98 W m−1K−1 and dielectric strength with 3.4. In addition, electrically insulating thermal interfaces demonstrate high-performing and reliable electrical systems under the dynamic load conditions. The surface temperature of heterogeneous ceramic-polymer encapsulated conductor is 17.8 °C lower than that of polymer-encapsulated conductor at the same electrical load. The findings shown here hold great promises for directing heat extraction in electrical machine systems, advancing thermal management for emerging electronic applications.

Dynamic ionic crosslinking, graft polyethylene glycol-based polymeric phase change materials networks with ultrahigh latent heat efficiency and recycling ability

Polymeric polyethylene glycol (PEG)-based phase change materials (PCMs) present the intrinsic shape-stable essence, tunable phase change properties and mechanical strength, yet most of polymeric PCMs present a relatively low latent heat density (<120 J/g) and efficiency (<0.7), non-recycling ability resulting from the covalent crosslinking structure. Herein, the graft PCMs (GPCMs) with graft PEG side chains were synthesized via the dynamic ionic crosslinking reaction of carboxyl-functionalized graft PEGs and citric acid as the carboxyl co-donors with divalent zinc cations. The phase change and rheological properties of the GPCMs can be readily tuned by the length of PEG side chains and the loading content of citric acid. The highest latent heat density and efficiency of the GPCMs reach up to 155.0 J/g and ∼1, respectively, resulting from the synergistic effect of the ionic bonding and graft PEG side chains. The GPCMs present the shape-stable solid-solid phase transition behavior, high thermal reliability and stability, photothermal properties by compositing carbon black and excellent solvent-induced dissolving ability resulting from the nature of dynamic ionic crosslinking. The design of dynamic ionic crosslinking GPCMs structure will provide a robust, versatile access to the combination of high latent heat density and efficiency, high mechanical strength, recycling ability in a single organic PCMs.