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Polyether-ether-2-ketone (PEKK) is a high-performance thermoplastic polymer used in various fields, from aerospace to medical applications, due to its exceptional mechanical and thermal properties. Nonetheless, the mechanical behavior of 3D-printed PEKK still deserves to be more thoroughly investigated, especially in view of its production by 3D printing, where mechanical properties measured at different scales are likely to be correlated to one another and to all play a major role in determining biomechanical properties, which include mechanical strength on one side and osteointegration ability on the other side. This work explores the mechanical behavior of 3D-printed PEKK through a multiscale approach, having performed both nanoindentation tests and standard tensile and compression tests, where a detailed view of strain distribution was achieved through Digital Image Correlation (DIC) techniques. Furthermore, for specimens tested up to failure, their fractured surfaces were analyzed through Scanning Electron Microscopy (SEM) to clearly outline fracture modes. Additionally, the internal structure of 3D-printed PEKK was explored through Computed Tomography (CT) imaging, providing a three-dimensional view of the internal structure and the presence of voids and other imperfections. Finally, surface morphology was analyzed through confocal microscopy. The multiscale approach adopted in the present work offers information about the global and local behavior of the PEKK, also assessing its material properties down to the nanoscale. Due to its novelty as a polymeric material, no previous studies have approached a multiscale analysis of 3D-printed PEKK. The findings of this study contribute to a comprehensive understanding of 3D-printed PEKK along with criteria for process optimization in order to customize its properties to meet specific application requirements. This research not only advances the knowledge of PEKK as a 3D-printing material but also provides insights into the multifaceted nature of multiscale material characterization. [ABSTRACT FROM AUTHOR]

Polymer materials are increasingly widely used in high-fire-risk applications, such as aviation interior components. This study aimed to compare the tensile, thermal, and flame-retardant properties of test samples made from ultra-performance materials, polyetherimide (PEI) and polyetherketoneketone (PEKK), using the fused filament fabrication process (FFF). The tensile tests were performed for these materials at different raster angles (0, 45, and 90°). The thermomechanical tests were done in the axial, perpendicular, and through-thickness directions to the extruded filaments. The impact of printing parameters on the flame retardancy of 3D-printed samples was investigated in vertical burn tests with varying specimen thicknesses and printing directions. Experimentally, it was testified that PEKK had better isotropic behaviour than PEI for mechanical performance, thermal expansion, and fire-resistant properties, which are essential in fabricating intricately shaped products. [ABSTRACT FROM AUTHOR]

In the present paper, the results of a research focused on microstructure investigation of steel welded joints by means of non destructive thermographic technique are presented. In particular, two rough joints obtained by means of irregular manual welding are analyzed. Active lock in thermography phase analysis is applied, basing on the evidence that thermal diffusivity is related to the thermal diffusion length, using the phase contrast trend as a function of the distance from the laser spot. Diffusivity is expected to be dependent on the local microstructure and vary through different directions. By the variation in diffusivity, it is possible to investigate the level of anisotropy.The results are compared with micrographic analysis. The proposed method provides an active lock-in infrared thermography analysis by means of a thermal camera and an exciting laser head to evaluate thermal diffusivity. [ABSTRACT FROM AUTHOR]

Temperature limitations in nickel‐base superalloys have resulted in the emergence of SiC‐based ceramic matrix composites as a viable replacement for gas turbine components in aviation applications. Higher operating temperatures allow for reduced fuel consumption but present a materials design challenge related to environmental degradation. Rare‐earth disilicates (RE2Si2O7) have been identified as coatings that can function as environmental barriers and minimize hot component degradation. In this work, single‐ and multiple‐component rare‐earth disilicate powders were synthesized via a sol‐gel method with compositions selected to exist in the monoclinic C 2/m phase (β phase). Phase stability in multiple cation compositions was shown to follow a rule of mixtures and the C 2/m phase could be realized for compositions that contained up to 25% dysprosium, which typically only exists in a triclinic, P1¯${\rm{\bar{1}}}$, phase. All compositions exhibited phase stability from room temperature to 1200°C as assessed by X‐ray diffraction. The thermal expansion tensors for each composition were determined from high‐temperature synchrotron X‐ray diffraction and accompanying Rietveld refinements. It was observed that ytterbium‐containing compositions had larger changes in the α31 shear component with increasing temperature that led to a rotation of the principal axes. Principal axes rotation of up to 47° were observed for ytterbium disilicate. The results suggest that microstructure design and crystallographic texture may be essential future avenues of investigation to ensure thermo‐mechanical robustness of rare‐earth disilicate environmental barrier coatings. [ABSTRACT FROM AUTHOR]

h-BN is a two-dimensional ceramic material with a lamellar structure, known for its typical orientation characteristics on mechanical and thermal properties. By optimizing the size and arrangement of h-BN grains in the matrix, the anisotropic characteristics of h-BN ceramics can be fully utilized to obtain ceramic materials with high thermal conductivity or high strength. In order to study the effect of grain orientation distribution on the mechanical and thermal properties of materials, the index of orientation distribution (IOP) was used to quantitatively characterize the orientation degree of h-BN grains and analyzed the effect of h-BN grain size on material properties. The results show when the initial h-BN size is 13.50 μm, the ceramic has the highest orientation degree/-507, and the mechanical and thermal properties show obvious anisotropy. While the related properties of BN-YAG ceramics varies significantly with the decrease of initial h-BN grain size. [ABSTRACT FROM AUTHOR]

This research focuses on four thermal characteristics of 3D products printed from the fourteen most common filaments. The softening temperature, coefficient of linear thermal expansion (CLTE), irreversible thermal strain, and thermal conductivity of the 3D printed samples at various measurement directions were evaluated, systematised, and analysed. Semi-crystalline and amorphous, electrically conductive and thermochromic polymer filaments were investigated. Four sets of samples were printed by the Ultimaker S5 3D printer. Printer settings provided the unidirectional orientation of all filament fibres in all specimens and uniform within any specimen's cross section to investigate the anisotropy of their properties. For investigation of the thermal characteristic of the 3D printed samples, thermomechanical analysis (TMA), differential scanning calorimetry (DSC) methods, and method for measurement of the thermal conductivity (Hot-Disk) were used. The penetration test showed that polyetherimide samples had the highest heat resistance, while the samples from polylactic acid (PLA) had the lowest one. The results of TMA demonstrated that the samples of polypropylene (PP), thermoplastic polyurethane (TPU), and Polyamide had the highest CLTE. In general, semi-crystalline polymers had a higher coefficient of thermal expansion than amorphous ones. During the TMA, almost all samples showed an irreversible thermal strain. PLA Red and Co-polyester showed significant shrinkage of 6–9% in the print direction and expansion in the build direction compared to other samples. Samples of PLA LAVA, acrylonitrile butadiene styrene, polycarbonate, PP, and TPU filaments demonstrated more stable thermal behaviour. The thermal conductivity analysis showed that almost all specimens had a certain degree of anisotropy. The highest thermal conductivity value was obtained for print direction for materials with pronounced anisotropic behaviour, except for polyamide samples. DSC study of post-printing relaxation of the structure of printed samples showed that rapidly cooled samples of semi-crystalline PLA material had a non-equilibrium structure with a low degree of crystallinity. Such structures changed with the time up to 400 h after printing, which also affected their stiffness and strength. The annealing of printed samples at temperatures of cold crystallisation allowed a significant increase in their crystallinity degree, thus approaching the upper limit of this degree for semi-crystalline PLA. [ABSTRACT FROM AUTHOR]

Polymer materials are increasingly widely used in high-fire-risk applications, such as aviation interior components. This study aimed to compare the tensile, thermal, and flame-retardant properties of test samples made from ultra-performance materials, polyetherimide (PEI) and polyetherketoneketone (PEKK), using the fused filament fabrication process (FFF). The tensile tests were performed for these materials at different raster angles (0, 45, and 90°). The thermomechanical tests were done in the axial, perpendicular, and through-thickness directions to the extruded filaments. The impact of printing parameters on the flame retardancy of 3D-printed samples was investigated in vertical burn tests with varying specimen thicknesses and printing directions. Experimentally, it was testified that PEKK had better isotropic behaviour than PEI for mechanical performance, thermal expansion, and fire-resistant properties, which are essential in fabricating intricately shaped products.

The design and long-term safety of geological repositories for high-level radioactive waste (HLW) are dependent on the precise determination of the thermophysical parameters of mudstone. However, there is no relevant literature on the study of the thermophysical properties of Tamusu mudstone, a prospective rock for HLW disposal in China under the complex HLW disposal conditions. Therefore, in this paper, Tamusu mudstone is examined, and its thermophysical properties are tested at temperatures in the range of 25–80 °C with and without the influence of external forces. The thermophysical parameters exhibited significant anisotropic characteristics and were strongly correlated with temperature. The increase in temperature increases the specific heat capacity while lowering the thermal diffusivity. Due to the external force, the anisotropy of the thermophysical parameters decreases, enhancing the ability of the mudstone to transfer thermal energy. Furthermore, the aforementioned phenomena were interpreted from a microscopic perspective. This work can aid in the thermal-related physical phenomena of argillaceous rock and provide key input parameters for both analytical and numerical modeling in the safety assessment of HLW repositories, and other underground facilities at high temperatures.

With the development of high-density electronics, polymer-based thermal conductive composites with excellent thermal and mechanical performance are receiving great attention. For the development of polymer-based thermal conductive composites with superior properties, it is essential to reduce the agglomeration of fillers and enhance the interfacial interactions between thermal conductive fillers and the polymer matrix. Among the several thermal conductive materials, graphene nanoplatelets (GNPs) and cellulose nanofiber (CNFs) are attracting attention. However, poor interfacial interaction between GNP and CNF leads to interfacial separation, which in turn, deteriorates its properties. Herein, we synthesized a pyranine-functionalized polyether dispersant (PyPE), which can significantly improve the interfacial interactions between GNPs and CNFs. The effect of PyPE on the dispersion behavior of GNPs and the thermomechanical properties of GNP-CNF composite were monitored. Furthermore, we also performed molecular dynamics (MD) simulations to investigate the impact of applying PyPE dispersant on the interfacial interactions between the GNPs and CNF matrix. The application of PyPE significantly enhanced the dispersibility of GNPs within the CNF matrix, resulting in a 15.5 % increase in-plane thermal diffusivity and a 24.5 % enhancement in tensile strength of the composite, demonstrating their potential applications in high power density electrical equipment and electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• A laser spot periodic heating technique based on sub-region phase fitting is developed in measuring the anisotropic thermal diffusivity of thin films. • The spatial distribution of phase is divided into linear and nonlinear regions for fitting in-plane and out-of-plane thermal diffusivity, respectively. • The thermal diffusivity of the tested films ranges from 5.5 × 10−8 m²/s to 9.6 × 10−4 m²/s. • The present method can accomplish anisotropic thermal diffusivity measurements for thin films with thicknesses ranging from a few to hundreds of microns. The thermal transport properties of thin films have garnered significant research interest due to their diverse applications in new energy sources and thermal management. As the thickness of anisotropic thin films decreases to a few microns, conventional laser flash analyzer and infrared lock-in thermography encounter difficulties in characterizing their thermophysical properties. In response to this challenge, we propose a laser spot periodic heating technique based on sub-region phase fitting for measuring anisotropic thin films. In this method, a thermocouple monitors the temperature response on the sample back surface, and the amplified voltage is subsequently measured using a lock-in amplifier to record the spatial distribution of the phase signal. Finite element simulations indicate that the impact of contact thermal resistance between the thermocouple and the sample can be negligible when measuring in variable locations. The anisotropic thermal diffusivity is then fitted using one-dimensional and three-dimensional unsteady-state heat conduction models, with the spatial distribution of phase lag being partitioned into linear and non-linear regions, respectively. We measure the in-plane and out-of-plane thermal diffusivity of a stainless-steel film, demonstrating the reliability and accuracy of the method. As a showcase study demonstrating the capabilities of our methodology, we test four anisotropic thin films, covering a large spectrum of thermal diffusivity, ranging from 5.5 × 10−8 m2/s to 9.6 × 10−4 m2/s. It is verified that the present method can accomplish anisotropic thermal diffusivity measurements for thin films with thicknesses ranging from a few to hundreds of microns, a capability crucial for advancing the characterization of the thermophysical properties of materials. [ABSTRACT FROM AUTHOR]

Composites with high out-plane thermal conductivity (TC) and great insulation are essential for thermal management in electronic devices. Herein, a transposable, highly thermal conductive silicone rubber (SR)/boron nitride (BN) composite was fabricated by multi-layer stacked hot pressing, in which the orientation of BN was enhanced based on rheological characterizations. Then the pre-pressed films were stacked under 180 °C to get a full-cured and thick composite. The enhanced orientation of BN and the excellent heat transfer capability of the composites were well verified by SEM, XRD, 2D WAXS, finite element analysis (FEA) and infrared thermography, which resulted in a wonderful thermal pathway and low interfacial thermal resistance. The TC of the composite reached 22.08 W/(m·K), and the high in-plane TC could be converted to high out-plane TC after simple vertically cut due to the flexibility and large thickness of composite. Meanwhile, for the first time, the excellent heat transfer capability of the composite was quantitatively characterized by the characteristic temperature rise time constant (τg). The rheological control was an efficient and potential strategy to get highly thermal conductive composites.

Sapphire crystals have a special lattice structure, which causes anisotropy in their processing quality due to anisotropy of the physical and mechanical properties. Laser-induced plasma assisted ablation (LIPAA) is a new processing technology used to process transparent, hard, and brittle materials. LIPAA is regarded as a photoelectric composite processing method that makes the material removal and surface generation mechanisms more complicated. In this study, a surface generated by LIPAA processing showed much higher quality than a surface generated by direct laser ablation. Moreover, LIPAA has the advantage of a lower etching energy threshold than that of infrared laser direct ablation. Infrared laser-induced plasma assisted ablation was performed on different sapphire crystal orientations to explore the influence of anisotropy on LIPAA processing. The LIPAA material removal rates for different sapphire planes were presented and compared with results for direct laser ablation-focused ion beam (FIB) processing. The results showed that thermal removal was most dominant during LIPAA processing of sapphire. The material removal rate was highest in the [10 1 ‾ 0] direction and lowest in the [11 2 ‾ 0] direction. [ABSTRACT FROM AUTHOR]

We examine the anisotropic electrical and thermal transport properties in single crystals of In2Te5 belonging to the monoclinic space group C12/c1 with the temperature gradient applied parallel (||) and perpendicular (⊥ ) to the crystallographic c-axis of the crystals. A systematic investigation of structural, electrical, and thermal properties suggests the role of layered structure in this material in guiding its thermoelectric behavior. The thermal conductivity along the c-axis (κ||c) was found to be smaller by a factor of 2 compared to the thermal conductivity along the direction perpendicular to the c-axis (κ ⊥ c ) over the entire temperature range. In contrast, the Seebeck coefficient along the c-axis (S||c) was found to be higher than its value along the direction perpendicular to the c-axis (S ⊥ c) . At room temperature, the figure of merit zT||c is found to be four times larger as compared to the figure of merit z T ⊥ c . Our results provide insights into how the resistivity, thermal conductivity, and thermopower depends on the crystalline anisotropy and its impact on the overall zT. [ABSTRACT FROM AUTHOR]

This work employs density functional theory for calculating the structural, mechanical, anisotropic, thermal, electronic, and optical properties of Ce1-xHfxO2 (x = 0, 0.25, 0.5, and 0.75) to explore the heavy substitutional doping effects of Hf. The cubic phase of CeO2 is transformed to tetragonal when 50% Ce is replaced by Hf. The computed formation energy and elastic constants demonstrate the phase stability of studied materials. The present calculation demonstrates the ductility of both undoped and Hf-doped CeO2, but the tetragonal Ce0.5Hf0.5O2 reveals highest ductility as compared to other phases. Moreover, the tetragonal phase is the most anisotropic one than that of other phases. Interestingly, both pure and doped phases are acceptable for thermal barrier coating, however doping with 75% Hf at Ce-site makes it even more suitable. The semiconducting nature of CeO2 is evolved because of having band gap in the electronic band structure, which is supported by its experimental report. The band gap is increased with increasing doping of Hf. The optical absorption and conductivity reconfirm the semiconducting nature of the titled materials. Furthermore, the overall optical nature predicts the efficient uses of Ce1-xHfxO2 in microelectronics, integrated circuits, and solar panel.

Efficiently thermal management in electronic devices calls for creating polymer composites that have superior thermal transport abilities. Compared with single-filler composites, hybrid-filler composites have gained significant attention as they not only utilize the advantages of each filler individually but also allow for the potential cooperation in constructing filler networks between them. Differing from the previous research on hybrid-filler size, geometry, composition, and content and their impact on thermal conductivity (TC) in composites, this study aims to examine the spatial distribution effects of hybrid-fillers. A binary-filler strategy comprising of anisotropic 2D h- BN and 0D isotropic S–Al 2 O 3 has been proposed, with the primary h -BN filler aligned to filly utilize its anisotropy and intrinsic TC properties. Furthermore, positioning a small quantity of S–Al 2 O 3 between adjacent parallel h -BN considerably improves TC in the non-oriented direction of silicon rubber (SiR) composites. A special focus is given to the influence of the interstitial S–Al 2 O 3 filler on the individual through-plane TC (λ ⊥) and in-plane TC (λ ⫽) variation of the binary-filler hybrid SiR composites, which are perpendicular and parallel to the oriented h -BN. When incorporating 40 vol% h -BN and 5 vol% S–Al 2 O 3 , the binary SiR composites exhibit the highest concurrent λ ⫽ and λ ⊥ values of 14.581 and 2.132 W/m·K, respectively. The corresponding effects on the ductility, hardness, and dielectric properties of the SiR composites were explained. Moreover, the use of commercially available TC fillers, along with the effortless preparation method, enables the potential to produce h -BN based TIMs materials on a large scale for thermal management usage. [Display omitted] • A binary filler system consisting in-plane oriented 2D h -BN and 0D isotropic S–Al 2 O 3 is designed. • The addition of S–Al 2 O 3 filler between adjacent parallel h -BN flakes facilitates vertical heat transfer. • The binary structure of h -BN/S–Al 2 O 3 exhibits an anisotropic feature in the filler contact thermal resistances. • The binary filler strategy mitigates the trade-off between in-plane and through-plane thermal conductivity. [ABSTRACT FROM AUTHOR]

The determination of the thermoelastic properties of polyimide (PI) fibers is important for their applications, however, these properties are difficult to measure directly, especially the transverse thermoelastic properties. Here, the transverse thermoelastic properties of PI fibers, including transverse Young's modulus (2.12 GPa), shear modulus (0.94 GPa), Poisson's ratio (0.05), and coefficient of thermal expansion (45.68 μm/m°C), were estimated by combining dynamic and static thermo-mechanical techniques, as well as various relevant micromechanical models. The transverse Young's modulus of PI fibers was only 1/46th of the longitudinal one, and the transverse coefficient of thermal expansion of PI fibers was positive, unlike the longitudinal one, which was negative, showing the typical anisotropy of PI fibers. Finally, the thermoelastic properties of the PI fibers were in turn used to predict the thermoelastic behavior of the PI fiber-reinforced composites, thus validating their effectiveness. [Display omitted] [ABSTRACT FROM AUTHOR]

Based on density functional theory, this paper uses first-principles methods to study the stability, electronic properties, anisotropy, thermodynamic properties, and optical properties of compound MB2 (M = V, Nb, Zr). The enthalpy of formation indicates that the compound MB2 is energy stable. Studying its electronic properties, it is concluded that the compound MB2 (M = V, Nb, Zr) has metallic properties from the band structure and density of states diagram. The analysis of the differential charge density shows that the binding force between B–M and M–M atoms is greater than that of B–B. The results of elastic performance research show that VB2, NbB2, and ZrB2 exhibit brittleness and are brittle materials. Moreover, VB2, NbB2, and ZrB2 also meet the mechanical stability standards. Research shows that the anisotropy of MB2 is: NbB2 > VB2 > ZrB2.The quasi-harmonic Debye model is used to study the thermodynamic properties of compound MB2 (M = V, Nb, Zr). We analyzed the change curve of heat capacity, volume, thermal expansion coefficient, and Debye temperature at 0–1600 K and 0–100GPa. According to the analysis of thermodynamic properties, MB2 also satisfies the thermal stability condition. Finally, this paper studies the absorption and reflection of light by MB2. It is found that absorption and reflection are relatively strong in the ultraviolet region. [ABSTRACT FROM AUTHOR]

Ceramics arematerials with goodmechanical properties; however, low fracture toughness, intrinsic brittleness and poor resistance against oxidation at high temperatures are challenges limiting their applications. TiB2Mo is a ceramicmaterial whose all elastic properties have not been calculated. In this study, we investigated the elastic, electronic and thermal properties of TiB2Mo structure using first principles calculations. All first principles calculations were based on the density functional theory as implemented in QuantumESPRESSO code with the help of Thermo_pw as a post-processing code. Obtained lattice parameters of TiB2Mo structure were in good agreement with other previous theoretical studies. TiB2Mo structure was found to bemechanically and dynamically stable at ground state conditions. The results also show that TiB2Mo is brittle, anisotropic andmetallic in nature. Based on the calculated Vicker's hardness Hv, we noted that TiB2Mo is classified as a hardmaterial with fracture toughness of above 7MPam0.5; therefore, it is a promising ultra-high temperature ceramic. [ABSTRACT FROM AUTHOR]

• Despite relatively weak hydrogen bonds, tetracarboxylic-based frameworks (TCFs), a three-dimensional (3D) HOF, show relatively high thermal conductivity. • Electrostatic interactions in TCFs dominate thermal conductivity and anisotropy but central atoms in the monomers show negligible impact. • Electrostatic interactions sustain phonon modes with frequencies of 5–25 THz to carry heat and are key to maintaining high crystallinity in TCFs. Hydrogen-bonded organic frameworks (HOFs), an emerging class of porous molecular materials assembled through hydrogen bonds (H-bonds), have shown intriguing latent for multifunctional materials or devices. Understanding thermal transport in HOFs is crucial to guiding the functional material design with desired thermal properties. Here, we report thermal transport properties in HOFs and reveal the significance of electrostatic interactions (H-bonds and π-π interactions) to heat conduction with molecular dynamics simulations. It is found that despite relatively weak H-bonds, tetracarboxylic-based frameworks (TCFs), a three-dimensional (3D) HOF, show relatively high thermal conductivity compared with known 3D porous covalent organic frameworks and metal-organic frameworks. Electrostatic interactions in TCFs dominate thermal conductivity and anisotropy but central atoms in the monomers show negligible impact. The structural analysis and x-ray diffraction patterns highlight the importance of electrostatic interactions in maintaining the high crystallinity of TCFs. The vibrational density of states and spectral thermal conductivity further demonstrate that phonon modes with frequencies below 25 THz contribute about 90 % of total thermal conductivity in TCFs, and electrostatic interactions sustain phonon modes with frequencies of 5–25 THz to carry heat. These findings provide a fundamental understanding of structure-thermal conductivity relation in HOFs and advance their applications for multifunctional materials and devices. [ABSTRACT FROM AUTHOR]

Highly anisotropic thermal conductivity, i.e., a limited through-plane thermal conductivity (λ ⊥), is normally observed in polymer composites with asymmetric fillers that are vulnerable to orientate along the flow field during melt-processing. We herein explored the possibility to tailor the filler arrangement and λ ⊥ of polymer composites with asymmetric fillers using nonconductive hollow glass microspheres (HGμS). The results showed that λ ⊥ of ultrahigh-filled polyamide 6/flake graphite (PA6/FG) composites with 70 wt% (54.7 vol%) FG increased by 27% instead of decreasing when replacing 3 wt% FG platelets with HGμS (i.e., 8.1 vol%, and 12.2 vol% HGμS with a diameter of 18 μm and 38 μm, respectively). The increase of λ ⊥ from diluting FG with HGμS was attributed to the reduced structural anisotropy of the FG network, i.e., the in-plane orientation of FG platelets within the polymer matrix was inhibited. A synergistic effect on the improvement of λ ⊥ was achieved by replacing FG platelets with combination of HGμS and alumina (Al 2 O 3) microspheres. This synergy takes the effects from the "bridging" of FG platelets by Al 2 O 3 and the inhibiting of in-plane FG orientation by HGμS. [Display omitted] [ABSTRACT FROM AUTHOR]

The rapid development of integrated circuits and electronic devices with increased power density and heat flux, requires effective heat dissipation for thermal management. Constructing a directional thermal pathway from the vertically aligned thermal conductive fillers in the thickness-direction of polymer-based thermal interface materials (TIMs) is a desirable strategy to form materials with high thermal conductivity. However, due to the complexity of vertical orientation technology, fillers with the poor orientation degree weaken the enhancement of through-plane thermal conductivity. In this work, we prepared short carbon fiber (CF)/olefin block copolymer (OBC) composites with high orientation degree via the melting extrusion method on a basis of sharing force induce alignment. Attributed to the high orientation degree of CF in the vertical direction, the as-prepared material shows a through-plane thermal conductivity (κ ⊥) up to 15.06 W/m K at a 30 vol% CF content, which is ∼10 times that of a parallel structure. The operating temperature difference between vertical and random reached 35.2 °C, surpassing the characters in most works of literature. This study provides an effective way to develop high-oriented degree and electrical insulation polymer composites with superior κ ⊥ for scalable thermal management applications in electronic devices. [Display omitted] • A facile and efficient method to obtain high orientation for polymer-based TIMs. • Excellent through-plane thermal conductivity is obtained via constructing vertical structure. • Outstanding thermal management capability is achieved as an efficient TIM. [ABSTRACT FROM AUTHOR]

Composites with high out-plane thermal conductivity (TC) and great insulation are essential for thermal management in electronic devices. Herein, a transposable, highly thermal conductive silicone rubber (SR)/boron nitride (BN) composite was fabricated by multi-layer stacked hot pressing, in which the orientation of BN was enhanced based on rheological characterizations. Then the pre-pressed films were stacked under 180 °C to get a full-cured and thick composite. The enhanced orientation of BN and the excellent heat transfer capability of the composites were well verified by SEM, XRD, 2D WAXS, finite element analysis (FEA) and infrared thermography, which resulted in a wonderful thermal pathway and low interfacial thermal resistance. The TC of the composite reached 22.08 W/(m·K), and the high in-plane TC could be converted to high out-plane TC after simple vertically cut due to the flexibility and large thickness of composite. Meanwhile, for the first time, the excellent heat transfer capability of the composite was quantitatively characterized by the characteristic temperature rise time constant (τ g). The rheological control was an efficient and potential strategy to get highly thermal conductive composites. • The silicone rubber (SR)/boron nitride (BN) composites with highly oriented BN were prepared by combining optimal pre-orientation based on rheological characterization and multilayer stacked hot pressing. • The enhanced orientation of BN and lower ITR were achieved at low viscosity (135 °C), and the TC of O-SR/BN 83.33 reached 22.08 W/(m·K). • The effect of BN with different degrees of orientation on the TC of the composite was further verified by SEM, XRD, 2D WAXS and FEA. • The excellent heat transfer capability of the composite was quantitatively characterized by the characteristic temperature rise time constant (τ g). [ABSTRACT FROM AUTHOR]

A facile strategy for effectively constructing in-plane and through-plane thermal conduction paths in polyimide (PI) and its flexible copper clad laminates (FCCLs) was reported by incorporation of hexagonal boron nitride (h-BN) in a controlled manner. The in-plane thermal conductivity pathways resulted from the micron h-BN sheets well mixed within the continuous PI matrix, while the through-plane ones were mainly constructed by the arrayed pillar-like or striped-like high concentration (65.2 wt%) h-BN nano-particles/thermoplastic polyimide (TPI) composites (acting as islands), which were distributed in the above micron PI/h-BN composite (acting as sea) and perpendicular to the direction of thickness. The specific sea-island architecture allowed the preparation of highly thermally conductive flexible PI film and its FCCLs at relatively lower total boron nitride loading. Balanced thermal conductivities and mechanical properties were achieved, for example, in the PI/h-BN composite film containing 30 wt% micron h-BN. The in-plane and through-plane thermal conductivities increased from 0.18 W m−1 K−1 and 0.15 W m−1 K−1 of neat PI film to 2.56 W m−1 K−1 and 0.57 W m−1 K−1, respectively. Meanwhile, the tensile strength and elongation at break can remain at 98.4 MPa and 8.7%. Interestingly, when the pillar-like high concentration h-BN nano-particles/PI composites were present, the in- and out-plane thermal conductivities of the composite films considerably increased to 5.03–6.32 and 1.27–1.29 W m−1 K−1, although the total BN content was only raised by ∼1 wt%. The results of the current work may open a new avenue for promoting the practical application of thermally conductive PI based FCCLs. [Display omitted] 1. High thermal conductive flexible copper clad laminate is made by a simple method. 2. Sea-island structured BN/PI composite favors improving bidirectional heat conduction. 3. Mayer rod coating coupled with hot pressing enhance orientation of BN platelets. [ABSTRACT FROM AUTHOR]

Ice-templated waxy maize starch. [Display omitted] • Neat anisotropic waxy maize starch cryogels were made via ice-templating method. • The morphology varied from lamellar to sponge-like, controlled by starch concentration. • Cryogels possess anisotropic mechanical and thermal conductivity properties. • Cryogel compression in the transverse direction leads to thermal conductivity decrease. Biodegradable anisotropic neat porous starch materials without any additional cross-linking, plasticizer or any extra matter have been fabricated via facile ice-templating method. Waxy maize was dissolved in water followed by unidirectional freezing and ice sublimation. The influence of process parameters (starch concentration and retrogradation time) on the morphology, density, mechanical properties under the uniaxial compression and thermal conductivity were investigated. The internal morphology and the shape of the pores, from lamellar to sponge-like, was shown to be governed by starch concentration. All porous starches have very low density (0.07–0.15 g/cm3), anisotropic mechanical properties and low thermal conductivity, in particular in transverse direction (0.037–0.048 W/(m·K)). Interestingly, when compressing the ice-templated starches in the transverse direction, the thermal conductivity was further decreased reaching the values of 0.033 W/(m·K). This work provides the guidelines for making fully biobased porous starch materials with controlled morphology and properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermodynamic and mechanical stability are manifested by the calculated formation energy and elastic constants. • Tetragonal Ce 0.5 Hf 0.5 O 2 is more ductile than cubic phases. • Tetragonal phase exhibits highest anisotropic nature among all the studied phases. • Band gap is increased with the increment of Hf doping level. • Optical functions suggest the potential applications of Ce 1-x Hf x O 2 in microelectronics, integrated circuits, and solar panel. This work employs density functional theory for calculating the structural, mechanical, anisotropic, thermal, electronic, and optical properties of Ce 1-x Hf x O 2 (x = 0, 0.25, 0.5, and 0.75) to explore the heavy substitutional doping effects of Hf. The cubic phase of CeO 2 is transformed to tetragonal when 50% Ce is replaced by Hf. The computed formation energy and elastic constants demonstrate the phase stability of studied materials. The present calculation demonstrates the ductility of both undoped and Hf-doped CeO 2 , but the tetragonal Ce 0.5 Hf 0.5 O 2 reveals highest ductility as compared to other phases. Moreover, the tetragonal phase is the most anisotropic one than that of other phases. Interestingly, both pure and doped phases are acceptable for thermal barrier coating, however doping with 75% Hf at Ce-site makes it even more suitable. The semiconducting nature of CeO 2 is evolved because of having band gap in the electronic band structure, which is supported by its experimental report. The band gap is increased with increasing doping of Hf. The optical absorption and conductivity reconfirm the semiconducting nature of the titled materials. Furthermore, the overall optical nature predicts the efficient uses of Ce 1-x Hf x O 2 in microelectronics, integrated circuits, and solar panel. [ABSTRACT FROM AUTHOR]

• A general experimental method is proposed to observe the heat conduction of soft materials as represented by hydrogels. • The effects of uniaxial loading on the anisotropy of thermal conductivity K and surface heat transfer coefficient H are investigated. • A microscopic statistical model is developed to characterize the stretch induced anisotropic thermal conduction of hydrogels. Soft materials involving both temperature and deformation, as represented by multi-functional hydrogels for temperature sensing and thermal actuation, have been widely mentioned in recent researches. In many circumstances, the hydrogels are working under combined actions of the thermal stimuli and the mechanical forces. The complex conditions require accurate experimental techniques in characterizing thermal and mechanical properties, and call for theoretical models to quantify the deformation dependent thermal properties. In this work, we proposed a novel experimental method to determine thermal conductivity and surface heat transfer coefficient in the hydrogel, using thermochromic capsule powders (TCPs) as an indicator for temperature change. A microscopic statistical model was developed for the hydrogel, to relate the anisotropy of the thermal conductivity to the deformation. The new model takes the hydrogel as a 3-phase composite and relates the stretch-induced orientation change of polymer chains to the change of thermal conductivity. Using the new experimental technique, we measured the thermal properties of PAAm in both hydrogel and dried network states, under different extension ratios. The model enables us to determine two microscopic scale thermal properties from the experimental data of the dried network, and predict the thermal conductivity of hydrogel under different stretches. The prediction accurately captures the stretch induced thermal conduction anisotropy of hydrogel and agrees well with the experimental results. [ABSTRACT FROM AUTHOR]

This paper reports on an experimental investigation on the mechanical degradation of carbon fiber reinforced composites (CFRP) subjected to long-term exposure of low-density electric field by passing direct current (DC) through cross-ply laminates. In this study, an in-house fabricated experimental setup is used to study the effects of long-duration electrical conduction through cross-ply CFRP laminates. The experiments are conducted under constant current conditions. The change in laminate resistance is measured by monitoring the voltage across the specimen. Meanwhile, the effects of Joule heating are measured by monitoring the surface temperature across the length of the composite sample. Both voltage and temperature measurements are made continuously through the duration of the experiment. Experiments are conducted for continuous three (3) and twenty-four (24) hour duration and for cyclic three-hour repeated duration. Combined loading-compression (CLC) mechanical testing, ultrasonic pulse-echo test and dynamic mechanical analysis (DMA) is performed after electrical degradation to quantify mechanical and thermo-physical changes in the material. It is found that the electrical degradation leads to a 13%–15% reduction in compressive strength, 6%–7% reduction in Young's modulus in thickness direction, 3%–4% decrease in glass transition temperature, and 41%–45% increase in tan δ. Post-degradation electrical resistivity change in through-thickness and in-plane directions is also correlated to damage. Comparison of change in resistivities of electrically degraded samples to thermally loaded samples indicates that the primary degradation is in the form of delamination caused by Joule heating and localized dielectric breakdown of epoxy near the carbon fiber–epoxy interface. Additionally, X-ray computed tomography (CT) images confirm that damage accumulated in electrically degraded samples is a combination of thermal damage due to Joule heating and dielectric degradation between plies due to passage of electric current. [ABSTRACT FROM AUTHOR]

• Unidirectional anisotropic PIAs have been prepared by freeze-drying. • The PIA shows excellent thermal stability and stable mechanical behavior. • The u -PIA-6 exhibits great strength, which is over twice as high as that of the TEEK-HH at 177 °C with a similar density. • The u -PIA shows great thermal insulation properties in anisotropic. Polyimide aerogels (PIAs) are the new type of high-performance lightweight material that combines the excellent thermal and mechanical behavior of polyimides with the highly porous and lightweight properties of aerogels. PIAs can meet the increasing material requirements of high-tech fields such as the aerospace and transportation industries. This study reports a series of all-aromatic anisotropic polyimide aerogels (p-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA)) with unprecedented behavior. These PIAs were synthesized using a random or unidirectional freeze-drying method followed by thermal imidization of the precursor solution. Their mechanical and thermal conductivity performance were anisotropic (u -PIA-8 strength: 1.86 and 0.14 MPa, thermal conductivity: 62.9 and 50.1 mW·m−1·K−1 along the axial and radial direction, respectively). Furthermore, the PIAs possessed excellent compression behavior in a wide temperature range from 25 °C to 316 °C, with a compressive strength over twice that of the commercial polyimide foam TEEK-HH (u -PIA-6 strength: 0.83 and 0.32 MPa at 177 and 316 °C, TEEK-HH strength: 0.31 MPa at 177 °C). These aerogels also demonstrated good thermal insulation performance after being held at 300 °C for 20 min (u -PIA-8: 76.3 °C at 25 mm). These highly anisotropic aerogels exhibit flexible thermal protection properties that extend the potential use of PIAs to applications such as high-temperature-resistant rocket fairings, sandwich structures, and arc-shaped structures for aerobats or the automobile industry. [ABSTRACT FROM AUTHOR]