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Thermal interface materials (TIMs) are vital to dissipate excess heat generated by electronic components with ever-growing power density to ensure their reliability and performance. However, the limited dispersibility of nano-sized thermal conductive fillers hinders further enhancement of thermal conductivity in TIMs. It remains challenging to manufacture high-performance TIMs with simultaneous high thermal conductivity, low cost, and capability of large-scale production. Herein, a solvent-free and scalable approach was adopted to fabricate asphalt/graphite nanoplatelets (GNPs) composites by in situ exfoliating graphite in asphalt melt using a three-roll mill. During exfoliation, asphalt was adsorbed onto the surface of GNPs via π-π interaction and improved their dispersibility. Hence, GNPs formed integrated thermal conductive pathways with reduced interfacial thermal resistance, which significantly improved the thermal conductivity of asphalt/GNP composites. At 25 vol% loading, the asphalt/GNP composite displayed a thermal conductivity of 1.95 W m−1 K−1, showing a 114 % increase compared to the asphalt/commercial GNP (c-GNP) composite prepared by conventional mechanical mixing. Moreover, the heat-resistant and mechanical properties of the asphalt/GNP composites were also enhanced due to the improved filler dispersion and filler-matrix interactions. Thus, the asphalt/GNP composites fabricated by in situ three-roll milling possessed remarkable advantages as TIMs compared with asphalt/c-GNP composites and commercial silicone rubber thermal pads. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Metal compound/graphene composites have been dominantly fabricated by in-situ intercalation of metal-containing precursors into graphene or graphene oxide (GO) followed by chemical and/or thermal treatment. This process usually leads to the formation of 0D oxide nanoparticles/2D graphene composites with the limited improvements in the supercapacitor performance. Herein a facile two-step method was reported to fabricate 3D porous Ni(OH) 2 /graphene composite hydrogels (NiGH) by incorporating the pre-synthesized 1D Ni(OH) 2 nanobelts into a GO suspension followed by the hydrothermal process. The resulted hydrogels show large specific surface area (370.6 m2/g) and can be directly used as the self-supported electrodes. The NiGH electrode exhibits the specific capacitance up to 1738.3 F/g at 10 mV/s and 1701.5 F/g at 1 A/g, retains 1385.0 F/g at 100 mV/s and 1152.0 F/g at 8 A/g, respectively. The capacitance and rate performance of NiGH are far superior to those of Ni(OH) 2 (841.2 F/g at 10 mV/s; 592.5 F/g at 1.0 A/g), graphene hydrogel (207.5 F/g at 10 mV/s), and the control Ni(OH) 2 nanoparticle/graphene composite powder (NiGP: 1045.8 F/g at 10 mV/s; 950.8 F/g at 1.0 A/g) prepared by the one-pot hydrothermal processing of Ni salt and GO. Meanwhile, the NiGH electrode also shows lower resistance and higher cycling stability (retaining 100.8% of initial capacitance over 5000 cycles at 5 A/g) as compared to Ni(OH) 2 , graphene hydrogel, and NiGP due to the efficient combination of pseudo-capacitive 1D Ni(OH) 2 nanobelts and conductive 2D graphene sheets to create 3D architectures. Such a facile two-step protocol enables the superiority of ultrathin oxide nanobelts to fabricate 3D graphene-based composite hydrogels for high-performance supercapacitor electrodes. Graphical abstract 3D Ni(OH) 2 nanobelt/graphene composite hydrogels were fabricated by incorporating the pre-synthesized Ni(OH) 2 nanobelts into a suspension of graphene oxide followed by hydrothermal treatment. The resulting self-supported electrodes show much better electrochemical performance compared to the powdery Ni(OH) 2 nanoparticle/graphene composites prepared by one-pot hydrothermal processing of Ni salts and graphene oxide. Image 1 Highlights • Combining quasi-1D Ni(OH) 2 nanobelts with 2D graphene to fabricate 3D hydrogels. • Free-standing electrodes with large specific surface area and ultrahigh capacitance. • Synergistic improvements in rate capability, interface resistance, and cyclability. [ABSTRACT FROM AUTHOR]

The effect of elastic modulus mismatch of epoxy/silver nanowires (epoxy/AgNWs) composites on thermal conductivity was critically evaluated by synthesizing a stiff titanium dioxide (TiO 2 ) coating on the surface of AgNWs (designated as AgNWs@TiO 2 ) with different length/diameter aspect ratio. Compared to epoxy/AgNWs composites, AgNWs@TiO 2 could be more uniformly dispersed in epoxy matrix. However, the TiO 2 intermediate layer with a higher elastic modulus increased the modulus mismatch with epoxy, exacerbating the interfacial phonon scattering, and the thermal conductivity of the epoxy/AgNWs@TiO 2 composites was decreased. Moreover, the epoxy/AgNWs@TiO 2 composites possessed enhanced volume electrical resistivity and reduced dielectric properties relative to the epoxy/AgNWs composites. These observed results on thermal conductivity, electrical insulation, dielectric loss and dielectric constant due to TiO 2 -coated AgNWs are more prominently displayed at higher nanowire loading (4 vol%) and aspect ratio (1000). [ABSTRACT FROM AUTHOR]

Interfacial tailoring is always the key to preparing high-performance polymer-based thermal conductive composites (PTCs). Herein, we reported a multi-functional interface tailoring approach to simultaneously improve the thermal conductivity, flame retardancy, thermal and mechanical properties of PTCs, by forming a core-shell structured graphene oxide coating Al 2 O 3 hybrid (Al 2 O 3 @HGO). Simultaneously a flame retardant bridging agent was introduced to improve the coating amount and flame retardant efficiency of the hybrid. The morphology analysis revealed the significant reinforcement of interfacial interaction of Al 2 O 3 in epoxy (EP) by HGO coating. As a result, such the interfacial tailoring induced both the significant decrease in interfacial thermal resistance and the formation of additional thermal conductive paths by the graphene coating layer, resulting in the significant improvement in thermal conductivity of EP/Al 2 O 3 @HGO composites. The flame retardant parameters, peak heat release rate, total heat release and total smoke production, showed a 49.3%, 40.9% and 71.2% reduction, respectively, comparing to neat EP, which was ascribed to the strong interface with GO coating layer and the flame retardant bridging agent catalyzed charring to form an intact and compact char protective layer with Al 2 O 3 . Moreover, the strong interfacial interaction also restricted the segment movement, increasing the storage modulus and T g . [ABSTRACT FROM AUTHOR]

A facile and effective approach by incorporating silica nanoparticles (SNPs) to fabricate high performance epoxy-based electronic packaging materials which are both thermally conductive and electrically insulating was presented. Because of the strong interaction between SNPs and silver nanowires (AgNWs), uniformly dispersed SNPs-modified epoxy was employed to promote the dispersion of AgNWs in epoxy matrix. Further, the enhanced modulus of epoxy matrix by the incorporation of SNPs effectively alleviates the modulus mismatch between stiff AgNWs and epoxy matrix. Compared with epoxy/AgNWs composites without SNPs, the resulting hybrid materials, that is, epoxy/SNP/AgNWs, showed distinct improvements in thermal conductivity without degrading their mechanical properties. Also, the SNPs were absorbed onto the surface of AgNWs forming an electrical insulation layer to disrupt the electron flows between adjacent AgNWs, hence retaining the electrical insulation of epoxy matrix. Finally, this new fabrication method is easily scalable owing to its simple procedure and use of commercial well-dispersed SNPs-modified epoxies. [ABSTRACT FROM AUTHOR]

Silver nanowires (AgNWs), as one-dimensional nanostructured materials, possess high aspect ratio and intrinsically high thermal conductivity. However, AgNWs are difficult to disperse homogeneously in epoxy resin, and their high electrical conductivity also limits their applications for electronic packaging. Herein, silica-coated silver nanowires (AgNWs@SiO 2 ) were synthesized by a flexible sol–gel method and then incorporated into epoxy. The less stiff silica intermediate nanolayer on AgNWs not only alleviated the mismatch between AgNWs and epoxy, but also enhanced their interfacial interaction. Hence, the thermal conductivity of an epoxy/AgNWs@SiO 2 composite with 4 vol.% filler loading was increased to 1.03 W/mK from 0.19 W/mK of neat epoxy compared to 0.57 W/mK of an epoxy/AgNWs composite with identical nanowire loading. Simultaneously, the insulating silica nanolayer effectively avoided formation of an electrically conductive network of AgNWs in epoxy, leading to high electrical insulation of the composite. AgNWs@SiO 2 nanowires with core–shell structure also improved the dielectric properties of epoxy. In addition, these composites possessed a viscosity suitable for the underfill process in electronic packaging. [ABSTRACT FROM AUTHOR]

Epoxy (EP) composites with comprehensive good processability, low coefficient of thermal expansion (CTE), and high thermal conductivity, but electrical insulation properties are largely demanded in the higher power electric devices. However, micro-fillers have a positive effect on maintaining the good flowability of epoxy composites, while do not bring high thermal conductivity enhancement per unit mass. While nano-fillers with high specific surfaces offer very promising opportunities for heat-conducting network construction, but the nano-fillers dispersion is difficult to control and will cause increased viscosity and processing difficulties. Herein, we expect that the addition of small amounts of silver nanowires (AgNWs) at 0.5 vol% into the EP/S-Al 2 O 3 composites could largely enhance the thermal conductivity but not sacrifice their processability. Owing to the bridging effects of rigid nanowires between the main spherical particles, the thermal conductivity of the micro-nano EP/AgNWs/ S -Al 2 O 3 composites with 40 vol% S -Al 2 O 3 and 0.5 vol% AgNWs exhibits a 106.5% increment comparing to that without AgNWs. The limitation of both single micro or nano-sized thermal conductive fillers can be offset by the micro-nano filler network structure. The best combination properties of the EP/AgNWs/ S -Al 2 O 3 composites can reach the high thermal conductivity (1.602 W/m·K), low viscosity (55.6 Pa s), low CTE (37.1 ppm/°C), and high glass transition temperature (T g , 152.1 °C). These results demonstrate that adding multiscale fillers into epoxy composites may solve the tradeoff between thermal conductivity and processability performances and fit the applications in high-power density electronic devices. The cost-effective epoxy-based underfill materials with high thermal conductivity play a critical role in the performance and reliability of rapidly developed microelectronic products. A novel epoxy composites with multiscale micro-nano filler structure are developed to overcome the limitation of only adding single micro- or nano-sized thermal conductive fillers to achieve higher thermal conductivity and better processibility simultaneously. [Display omitted] [ABSTRACT FROM AUTHOR]

Holographic polymer nanocomposites have drawn considerable attention due to their unique capability of reconstructing colored three-dimensional (3D) images identifiable to the naked-eye. Yet, it still remains challenging to add more and orthogonal (i.e. , data access without crosstalk) optical functions to current holographic polymer nanocomposites. Herein, we design and demonstrate a holographic polymer nanocomposite with robust optical diffraction and upconversion photoluminescence. This paradigm is enabled by controlling the spatial location of upconversion nanorods (UCNRs) in the constructive (polymer-rich) regions during holographic recording, while utilizing the phase separating liquid crystal (LC) in the destructive regions to boost the refractive index difference between the constructive and destructive regions. One identical holographic image is reconstructed and readily visible to the naked-eye under ambient light, whereas four different covert luminescence states (i.e. , none, blue, yellowish green and red emissions, respectively) can only be distinguishable upon the 980 nm laser illumination. The double-verifiable and crosstalk-free optical features pave a way to design new tags with orthogonal optical functions for anti-counterfeiting and security applications. [ABSTRACT FROM AUTHOR]