Jinhong Yu

Permittivity, thermal conductivity and thermal stability of poly(vinylidene fluoride)/graphene nanocomposites

Poly(vinylidene fluoride) (PVDF)/graphene nanocomposites were prepared by solution blending. The incorporation of graphene sheets (GSs) increased the permittivity, thermal conductivity and thermal stability of PVDF, resulting in a transition from electrical insulator to semiconductor with a percolation threshold of 4.5 wt%. The composite containing 7.5% GSs had a permittivity higher than 300 at 1000 Hz, which is about 45 times that of pure PVDF. The thermal conductivity of the composite with 0.5% GSs was increased by approximately a factor of 2 when compared with the pure PVDF. The addition of 0.05% GSs produced an increase in the maximum decomposition temperature of PVDF of over 20°C.

Alumina-coated graphene sheet hybrids for electrically insulating polymer composites with high thermal conductivity

Graphene has attracted considerable attention as a promising candidate to improve the thermal conductivity of polymers owing to its extremely high intrinsic thermal conductivity (∼5300 W m−1 K). However, graphene-based composites show a high electrical conductivity even with a low loading of fillers, which greatly limits their applications in electronic devices. Herein, we present a new class of fillers of alumina-coated graphene sheet (GS@Al2O3) hybrid fillers via an electrostatic self-assembly route. This unique structural design combines the advantages of both the GS and Al2O3, resulting in PVDF/GS@Al2O3 composites that show not only high thermal conductivity, but also retain high electrical insulation. For instance, the thermal conductivity of PVDF composites with 40 wt% GS@Al2O3 is up to 0.586 W m−1 K and the volume resistivity is above 4 × 1014 Ω cm. Moreover, this self-assembly route is a simple and scalable strategy for fabricating high performance thermally conductive materials.

Enhanced thermal conductivity for polyimide composites with a three-dimensional silicon carbide nanowire@graphene sheets filler

A rigid three-dimensional structure composed of silicon carbide (SiC) nanowire@graphene sheets (3DSG) was prepared using a high frequency heating process. The polyamide acid was then infused into the three-dimensional structure and imidized at 350 °C. The thermal conductivity of polyimide (PI)/3DSG composites with 11 wt% filler addition can be up to 2.63 W m−1 K−1, approximately a 10-fold enhancement when compared with the results obtained using neat PI. Furthermore, the 3DSG shows a better synergistic effect in thermal conductivity improvement, relative to a simple mixture of SiC nanowires and graphene sheets (GSs) fillers with the same additive content. The reinforced thermal properties can be attributed to the formation of efficient heat conduction pathways among GSs.

Preparation of hyperbranched aromatic polyamide grafted nanoparticles for thermal properties reinforcement of epoxy composites

Epoxy nanocomposites with hyperbranched aromatic polyamide grafted alumina (Al2O3) nanoparticles as inclusions were prepared and their thermal properties were studied. The Al2O3 nanoparticles were firstly treated with a silane coupling agent to introduce amine groups, then grafting of the hyperbranched aromatic polyamide started from the modified surface. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR) analysis proved hyperbranched aromatic polyamide grafted Al2O3 nanoparticles were successfully prepared by solution polymerization. Transmission electron microscopy (TEM) showed that there was a thin polymer layer on the Al2O3 nanoparticles surface, which contributes to the uniform dispersion of Al2O3 nanoparticles in epoxy matrix and the improvement of the interfacial interaction between Al2O3 nanoparticles and epoxy matrix. Thus the glass transition temperature, thermal stability, thermal conductivity and thermomechanical properties of nanocomposites were enhanced.

Enhancing the thermal and mechanical properties of epoxy resins by addition of a hyperbranched aromatic polyamide grown on microcrystalline cellulose fibers

In this study, microcrystalline cellulose fibers (MCFs) derived from sisal were treated with a hyperbranched aromatic polyamide (HBAP). The modified sisal fibers were used to produce composites with epoxy resins. Firstly the MCFs were treated with a silane coupling agent, then a HBAP was grown on the modified surface. The HBAP-MCFs were used to reinforce epoxy resins. The HBAP-MCF/epoxy composites were studied by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and mechanical properties analysis. The results show that the HBAP-MCFs enhanced the thermal and mechanical properties of the epoxy resin. For instance, the impact strength, tensile strength, Youngs modulus and toughness of the HBAP-MCF/epoxy composites with 2.0 wt% HBAP-MCFs were 32.1 kJ m−2, 59.4 MPa, 695 MPa, and 4.37 MJ m−3. These values represent improvements of 83.4%, 34.7%, 25%, and 178.3%, respectively, compared to a neat epoxy resin. Moreover, the addition of HBAP-MCFs produced composites with higher thermal degradation temperatures and glass transition temperatures. The HBAP-MCF swere effective in improving the thermal and mechanical properties due to a strong affinity between the fillers and the matrix.

Influence of interface chemistry on dielectric properties of epoxy/alumina nanocomposites

AbstractAlumina (Al2O3) nanoparticles with three different interface structures have been selected as reinforcement fillers for epoxy nanocomposite, that is surface untreated Al2O3 nanoparticles, γ-aminopropyl-triethoxysilane modified Al2O3 nanoparticles (Al2O3-APS), and hyperbranched aromatic polyamide grafted Al2O3 nanoparticles (Al2O3-HBP). The interface structures of the Al2O3 nanoparticles were characterized by X-ray diffraction and atomic force micrographs. Our studies reported the influence of the interface structure of Al2O3 nanoparticles on the morphology and dielectric properties of epoxy nanocomposites. It was found that the incorporation of the Al2O3-APS and Al2O3-HBP nanoparticles not only improved the dispersion of the nanoparticles in the epoxy matrix, but also enhanced the glass transition temperatures (Tgs) and largely influenced the dielectric properties of the epoxy nanocomposites as compared with the nanocomposites filled with the surface untreated Al2O3 nanoparticles. The improvement of Tgs, volume resistivity, dielectric strength, and the reduction of dielectric loss could be attributed to the good dispersion and special interface structure of the Al2O3 nanoparticles in the epoxy matrix.

Exceptionally high thermal and electrical conductivity of three-dimensional graphene-foam-based polymer composites

Graphene foams (GF) assembled with one- or few-layered ultrathin two-dimensional crystals have showed huge application potentials owing to their unique three-dimensional (3D) structure and superior properties. Here, we present a polymer-template-assisted assembly strategy for fabricating a novel class of 3D graphene architecture. A free-standing GF architecture has been built to act as thermal and electrical conduction paths in polymer composites. The obtained GF/polymer composites exhibit a high thermal conductivity (1.52 W mK−1) and high electrical conductivity (3.8 × 10−2 S cm−1) at relatively low GF loading (5.0 wt%). The GF/polymer composites are potentially useful in advanced packaging materials of high power LED and microelectronic devices.

Epoxy nanocomposites filled with thermotropic liquid crystalline epoxy grafted graphene oxide

Thermotropic liquid crystalline with epoxy groups grafted graphene oxide (LCE-g-GO) was synthesized by graphene oxide (GO), hexamethylene diisocyanate (HDI), and 4,4′-bis-(2-hydroxyhexoxy) biphenyl (BP2) by using pyridine and dibutyltin dilaurate as catalyst and dimethylformamide (DMF) as solvent. In this work, the LCE-g-GO nanosheets were characterized by Fourier transform infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and polarizing optical microscopy (POM). The epoxy nanocomposites were fabricated by incorporating different LCE-g-GO loading using cast molding method. The results revealed that the incorporation of the LCE-g-GO resulted in a significant improvement in thermal and mechanical properties. The epoxy nanocomposite with 5 wt% LCE-g-GO produced an increase in the temperature for 5 wt% weight loss (T5%) by 47 °C and glass transition temperature (Tg) by 14 °C when compared with the neat epoxy. Moreover, at the addition of 5 wt% LCE-g-GO, the impact strength of the epoxy nanocomposite is 35.06 kJ m−2, which is 2 times higher than that of the neat epoxy resin (17.49 kJ m−2). Meanwhile, the tensile strength of the nanocomposite is significantly increased to 92.5 MPa from 54.3 MPa, while the elongation at break is also increased to 42.9% from 25.7% of the neat epoxy, respectively. Therefore, the presence of the LCE-g-GO in the epoxy matrix could make epoxy not only stronger but also tougher.

Enhanced mechanical and thermal properties of epoxy with hyperbranched polyester grafted perylene diimide

A new kind of reactive toughening agent, named H20-g-PDI, has been successfully synthesized via hyperbranched polyester (H20) grafted to perylene diimide (PDI). The chemical structure of H20-g-PDI was characterized by Fourier transformed infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), wide angle X-ray diffractometry (WAXD), respectively. The H20-g-PDI was used as a toughening agent to enhance the mechanical and thermal properties of the epoxy resin. The morphology, mechanical and thermal properties of the composite was systematically investigated. The experimental results revealed that the impact strength, tensile strength, flexural strength and flexural modulus of the epoxy resin modified by H20-g-PDI reached the highest values of 47.6 KJ m−2, 93.19 MPa, 128.8 MPa, and 2205 MPa, respectively. These were 81.33%, 68.1%, 62.0%, and 19.8% higher than the neat epoxy when the content of H20-g-PDI loading reached 1.5 wt%. In addition, the glass transition temperature (Tg) and thermal stability of the epoxy composite was also enhanced. Tg and the decomposition temperature (Td) of the epoxy composite was about 20 °C and 27 °C higher than the neat epoxy, respectively. It is suggested that the formation of H20-g-PDI is effective to enhance the mechanical and thermal properties due to the homogeneous dispersion and strong interaction between the H20-g-PDI and the epoxy matrix.

In situ formation of a cellular graphene framework in thermoplastic composites leading to superior thermal conductivity

Based on the fast growth of the device performance, there has been an increasing demand for handling the issue of thermal management in electronic equipments. Therefore, it is of great significance to improve the thermal conductivity of thermoplastics, which are commonly used in electronic components. However, the difficulty of graphene dispersion and strong interfacial phonon scattering restrict the heat dissipation performance of graphene/thermoplastic composites, especially in the case of polypropylene (PP) or polyethylene (PE). Here, we propose a single-step and versatile approach to fabricate graphene/thermoplastic composites with a remarkable thermal conductivity enhancement. The composites were prepared by coating graphene on polymer powder first, followed by hot pressing. As a result, an interconnected graphene framework can be developed in the thermoplastic matrix, leading to significant heat transfer enhancement of the composites. At a 10 wt% graphene content, the thermal conductivity reaches 1.84, 1.53, 1.43, and 1.47 W m−1 K−1 for PE, PP, PVA (poly(vinyl alcohol)), and PVDF (poly(vinylidene fluoride)) composites, respectively. Our finding provides a path to develop a variety of highly thermally conductive thermoplastic composites for use in heat dissipation and other thermal applications.