Significantly Enhancing Mechanical and Thermal Properties of Cellulose-Based Composites by Adding Small Amounts of Lysozyme-Modified Graphene Nanoplatelets via Forming Strong Double-Cross-Linked Interface Interactions.

Thermally conductive cellulose-based composites have great application potential in the thermal management of portable and wearable electronic devices. In this work, cellulose-based composites with excellent mechanical and thermal properties were developed by using lysozyme-modified graphene nanoplatelets (LmGNP), epichlorohydrin (ECH), and hydrolyzed cellulose via forming strong double-cross-linked interface interactions, including the hydrogen bond network generated between LmGNP and cellulose and the chemical cross-link of ECH. As for the composites containing 8 wt % LmGNP, the in-plane thermal conductivity was 3.341 W·m-1K-1, while the tensile stress was 114.60 MPa, which increased by 297.3 and 146.2%, respectively, compared to pure cellulose. Along with the good stability, insulation, and lightweight properties, the fabricated composites have the potential to become a promising heat dissipation material for wearable electronic devices.

Anisotropic Thermally Conductive Perfluoroalkoxy Composite with Low Dielectric Constant Fabricated by Aligning Boron Nitride Nanosheets via Hot Pressing.

Thermal management has become a critical challenge in electronics and portable devices. To address this issue, polymer composites with high thermal conductivity (TC) and low dielectric property are urgently needed. In this work, we fabricated perfluoroalkoxy (PFA) composite with high anisotropic TC and low dielectric constant by aligning boron nitride nanosheets (BNNs) via hot pressing. We characterized the thermal stability, microstructure, in-plane and through-plane TCs, heat dissipation capability, and dielectric property of the composites. The results indicate that the BNNs-PFA composites possessed good thermal stability. When the BNNs content was higher than 10 wt %, the BNNs were well layer aligned in the PFA matrix, and the composites showed obvious anisotropic TC. The in-plane TC and through-plane TCs of 30 wt % BNNs-PFA composite were 4.65 and 1.94 W m-1 K-1, respectively. By using the composite in thermal management of high-power LED, we found that alignment of BNNs in composite significantly improves the heat dissipation capability of composite. In addition, the composites exhibited a low dielectric property. This study shows that hot pressing is a facile and low-cost method to fabricate bulk composite with anisotropic TC, which has wide applications in electronic packaging.

Graphene-Perfluoroalkoxy Nanocomposite with High Through-Plane Thermal Conductivity Fabricated by Hot-Pressing.

With the rapid development of electronics and portable devices, polymer nanocomposites with high through-plane thermal conductivity (TC) are urgently needed. In this work, we fabricated graphene nanosheets-perfluoroalkoxy (GNs-PFA) composite sheets with high through-plane TCs via hot-pressing followed by mechanical machining. When the GNs content exceeded 10 wt%, GNs were vertically aligned in the PFA matrix, and the through-plane TCs of nanocomposites were 10-15 times higher than their in-plane TCs. In particular, the composite with 30 wt% GNs exhibited a through-plane TC of 25.57 W/(m·K), which was 9700% higher than that of pure PFA. The composite with 30 wt% GNs was attached to the surface of a high-power light-emitting diode (LED) to assess its heat-dissipation capability. The composite with vertically aligned GNs lowered the LED surface temperature by approximately 16 °C compared with pure PFA. Our facile, low-cost method allows for the large-scale production of GNs-PFA nanocomposites with high through-plane TCs, which can be used in various thermal-management applications.

Determining the Surface Tension of Two-Dimensional Nanosheets by a Low-Rate Advancing Contact Angle Measurement.

Because of their atomic thinness, two-dimensional (2D) nanosheets need be bound to a substrate or be dispersed in material in various applications. The surface tension (ST) of a 2D nanosheet is critical for analyzing the physicochemical interactions between 2D nanosheets and other materials. To date, the determination of the ST of 2D nanosheets has relied mainly on the contact angle (CA) method. However, because of the difficulty in measuring the thermodynamically significant Young?s CA, which is the only meaningful CA that can be used to determine the ST, significant differences exist in reported STs of 2D nanosheets. In this study, we obtained such unique Young?s CAs on graphene, boron nitride, molybdenum disulfide, and tungsten disulfide nanosheets by a low-rate advancing contact angle measurement using a rigorously designed experimental setup. By interpreting the CA with Neumann?s equation of state, we determined the STs of these four nanosheets to be 29.7 ? 0.6, 30.9 ? 0.7, 27.8 ? 0.7, and 29.1 ? 0.8 mJ/m2, respectively. The surface energies of these 2D nanosheets were estimated to be in the range 95?120 mJ/m2 by considering the contribution of ST and surface entropy. The accuracy of these determined STs was validated by the exfoliation and dispersion of 2D nanosheets in liquids with a series of STs. The study may have important implications for understanding the physicochemical interactions between 2D nanosheets and other materials and the development of 2D nanosheet-based devices.

Effects of Tip Sonication Parameters on Liquid Phase Exfoliation of Graphite into Graphene Nanoplatelets.

Graphene nanoplatelets (GNPs) can be produced by exfoliating graphite in solvents via high-power tip sonication. In order to understand the influence of tip sonication parameters on graphite exfoliation to form GNPs, three typical flaked graphite samples were exfoliated into GNPs via tip sonication at power of 60, 100, 200, or 300 W for 10, 30, 60, 90, 120, or 180 min. The concentration of GNP dispersions, the size and defect density of the produced GNPs, and the sedimentation behavior of GNP dispersions produced under various tip sonication parameters were determined. The results indicated that the concentration of the GNP dispersions was proportional to the square root of sonication energy input (the product of sonication power and time). The size and ID/IG values (determined by Raman spectrum) of GNPs produced under various tip sonication powers and times ranged from ~ 1 to ~ 3 µm and ~ 0.1 to ~ 0.3, respectively, which indicated that all the produced GNPs were of high quality. The sedimentation behavior of GNP dispersions showed that the dispersions were favorably stable, and the concentration of each GNP dispersion was ~ 70% of its initial concentration after sedimentation for 96 h. Moreover, the TEM images and electron diffraction patterns were used to confirm that the produced GNPs were few-layer. This study has important implications for selecting the suitable tip sonicating parameters in exfoliating graphite into GNPs.

Thermal property improvement of polytetrafluoroethylene nanocomposites with graphene nanoplatelets.

Thermal properties including the crystallization behavior, thermal stability and thermal conductivity for a series of graphene nanoplatelet (GNP)-polytetrafluoroethylene (PTFE) nanocomposites were studied. The GNP-PTFE nanocomposites were fabricated via solvent-assisted blending followed by cold-pressing and sintering. The results indicated that the GNP-PTFE nanocomposites retained the good thermal stability of the PTFE matrix, and possessed better crystallization and much higher thermal conductivity than pure PTFE. The thermal conductivity of PTFE nanocomposites with a GNP mass fraction of 20% could reach 4.02 W (m K)-1, which was increased by 1300% compared with pure PTFE. Additionally, a theoretical model was proposed to analyze the thermal conductivity of GNP-PTFE nanocomposites. It is demonstrated that adding GNPs into PTFE homogeneously can effectively improve the thermal properties of the nanocomposites.

[Effect of PEG stress on plantlets of Chrysanthemum morifolium induced by endophytic botrytis sp. (C1) and Chaetomium globosum (C4)].

The effect of the endophytic fungi Botrytis sp. (C1) or Chaetomium globosum (C4) on the drought resistance of Chrysanthemum morifolium was studied. Ch. morifolium plantlets were inoculated with C1, C4 and cultured in the pots for 60 days, then the plantlets were stressed by 0%, 10%, 20%, 30%, 40% PEG6000 respectively in order to simulate different drought conditions. Biomass, the activities of SOD, POD, PAL, the contents of MDA and soluble protein of each group were determined. The results showed that endophytic fungi groups grew better than the control (without inoculation endophytic fungi). With the increasing of the concentration of PEG6000, the biomass of Ch. morifolium of each groups decreased, while the biomass of fungi groups was significantly higher than that of control, moreover C4 group higher than C1 group. With the concentration of PEG increasing, the content of MDA of each group increased too, while POD activity and soluble protein content of all treatments increased at first and then decreased. SOD activity and PAL activity of the control were increased with the increase of PEG concentration, but SOD activity of the two fungi groups were stable. After been stressed by different concentrations of PEG, MDA content of two fungi groups were always lower than the control, while SOD activity, POD activity, PAL activity and soluble protein content were higher. In conclusion, endophytic fungi can increase the drought resistance of Ch. morifolium.

[The effect of different endophytic fungi on Chrysanthemum morifolium output and quality].

OBJECTIVE: To enhance the flowers yield of Chrysanthemum morifolium by endophytic fungi. METHODS: Endophytic fungi (Chaetomium globosum strain C4 and Botrytis sp. strain C1) were inoculated to the plantlets which were planted in the pots. The output of the flowers was measured, the total flavonoids and essential oil contents of the flowers were determined. RESULTS: Compared to that of the control, fresh and dry outputs of the fungi C4 group increased 24.81%, 7.59%, fresh and dry outputs of the fungi C1 group increased 17.08%, 6.87%. Total flavonoids content of the fungi C4 group was higher than that of the control remarkably, fungi C4, C1 groups flowers total flavonoids content increased 31.79%, 8.55% compared to that of the control. Essential oil content of the fungi C4, C1 groups increased 13.21%, 18.19% respectively. The content percentage of various essential oil components of the fungi C4, C1 groups increased 10.42%, 8.90% compared to that of the control respectively. There were differences among the content percentage of various essential oil components of fungi C4, C1 treated group and the control's. CONCLUSION: The two fungi could build the symbiosis relation with the Chrysnthemum morifolium, which may cause them to enhance the output and quality finally.