Lidong Tian

High thermal conductivity graphite nanoplatelet/UHMWPE nanocomposites

High thermal conductivity graphite nanoplatelet/ultra-high molecular weight polyethylene (GNPs/UHMWPE) nanocomposites are fabricated via mechanical ball milling followed by a hot-pressing method. The GNPs are located at the interface of the UHMWPE matrix. The thermal conductivity coefficient of the GNPs/UHMWPE nanocomposite is greatly improved to 4.624 W m−1 K−1 with 21.4 vol% GNPs, 9 times higher than that of the original UHMWPE matrix. The significantly high improvement of the thermal conductivity is ascribed to the formation of multidimensional thermally conductive GNPs–GNPs networks, and the GNPs have a strong ability to form continuous thermally conductive networks. The method of cooling-pressing on the machine is more beneficial for the improvement of the thermal conductivity, by increasing the crystallinity of the UHMWPE matrix. Furthermore, the thermal stabilities of the GNPs/UHMWPE nanocomposites are increased with increasing addition of GNPs.

Hyperbranched polysiloxane (HBPSi)-based polyimide films with ultralow dielectric permittivity, desirable mechanical and thermal properties

Low-dielectric polyimide (PI) is on high demand in the next generation of high-density and high-speed integrated circuits. The introduction of fluorine or pores into PIs has been reported to efficiently obtain low-dielectric properties, but unavoidably deteriorate the mechanical and/or thermal properties. Therefore, it is a great challenge for PI to decrease its Dk and simultaneously maintain its mechanical and thermal properties. Herein, a series of robust PI films were fabricated by copolymerizing amine-functionalized hyperbranched polysiloxane (HBPSi) with pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA). The outstanding dielectric properties were achieved in a 35 wt% HBPSi PI film, which exhibits a Dk as low as 2.24 (1 MHz), mainly owing to the enhanced free volume and dielectric confinement effect afforded by the bulky HBPSi. Meanwhile, 35 wt% HBPSi PI demonstrates remarkable thermal stability and admirable mechanical properties, with the glass transition temperature of 388 °C, 5% weight loss temperature in argon flow up to 554 °C, a tensile strength of 80.6 MPa, elongation at break of 13.7% and a tensile modulus of 1.36 GPa. It also demonstrates conspicuous film homogeneity and planarity with the surface roughness as low as 0.42 nm and good moisture resistance with water uptake less than 1.5%. The prominent comprehensive properties make HBPSi PI a strong candidate for the future interlayer dielectrics.

Application of yolk–shell Fe3O4@N-doped carbon nanochains as highly effective microwave-absorption material

Yolk–shell Fe3O4@N-doped carbon nanochains, intended for application as a novel microwave-absorption material, have been constructed by a three-step method. Magnetic-field-induced distillation-precipitation polymerization was used to synthesize nanochains with a one-dimensional (1D) structure. Then, a polypyrrole shell was uniformly applied to the surface of the nanochains through oxidant-directed vapor-phase polymerization, and finally the pyrolysis process was completed. The obtained products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and thermogravimetric analyses (TGA) to confirm the compositions. The morphology and microstructure were observed using an optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The N2 absorption–desorption isotherms indicate a Brunauer–Emmett–Teller (BET) specific surface area of 74 m2/g and a pore width of 5–30 nm. Investigations of the microwave absorption performance indicate that paraffin-based composites loaded with 20 wt.% yolk–shell Fe3O4@N-doped carbon nanochains possess a minimum reflection loss of −63.09 dB (11.91 GHz) and an effective absorption bandwidth of 5.34 GHz at a matching layer thickness of 3.1 mm. In addition, by tailoring the layer thicknesses, the effective absorption frequency bands can be made to cover most of the C, X, and Ku bands. By offering the advantages of stronger absorption, broad absorption bandwidth, low loading, thin layers, and intrinsic light weight, yolk–shell Fe3O4@N-doped carbon nanochains will be excellent candidates for practical application to microwave absorption. An analysis of the microwave absorption mechanism reveals that the excellent microwave absorption performance can be explained by the quarter-wavelength cancellation theory, good impedance matching, intense conductive loss, multiple reflections and scatterings, dielectric loss, magnetic loss, and microwave plasma loss.

Novel Reusable Porous Polyimide Fibers for Hot-oil Adsorption

The development of oil sorbents with high thermal stability, adsorption capacity, reusability and recoverability is of great significance for hot oil leakage protection, especially for oil spillage of oil refinery, petrochemical industry and cars. In our work, highly efficient hot oil adsorption of polyimide (PI) fibers with excellent thermal stability was successfully prepared by a facile electrospinning method followed by post-treatment. The corresponding morphologies, structures and oil adsorption properties of as-prepared PI fibers at different temperatures were analyzed and characterized. Results showed that PI fibers presented a stable morphology and pore structure at 200°C. The oil adsorption capacity of porous PI fibers for hot motor oil (200°C) was about 57.4gg-1, higher than that of PI fibers (32.7gg-1) with non-porous structure for the motor oil at room temperature. Even after ten adsorption cycles, porous PI fibers still maintained a comparable oil sorption capacity (oil retention of 4.2%). The obtained porous PI fibers exhibited excellent hot oil adsorption capacity, reusability and recoverability, which would broaden the application of electrospun fibers in oil spill cleanup and further provide a versatile platform for exploring the technologies of nanofibers in hot oil adsorption field.