Jintang Zhou

Small magnetic Co-doped NiZn ferrite/graphene nanocomposites and their dual-region microwave absorption performance

In this study, novel CNZF (Co-doped Ni–Zn ferrite)/GN (graphene) nanocomposites were prepared by using a facile one-pot hydrothermal method. The phase structure, morphology, and magnetic and electromagnetic performance of the nanocomposites were studied by means of modern measurement techniques. Both sides of the GN sheets were densely covered by CNZF nanoparticles. Moreover, the magnetic nanoparticles had a uniform distribution without the presence of significant agglomeration. The electromagnetic performance indicated that the content of GN played a significant role in determining the dielectric behavior and magnetic anisotropy of the carbon materials, which further influenced the impedance matching and attenuation ability of absorbers. The microwave absorption properties showed that the CNZF/GN-10 nanocomposite exhibited dual-region microwave absorption, with two strong reflection loss peaks of −53.5 dB and −58.3 dB at 9.6 GHz and 5.2 GHz, respectively. The effective absorption bandwidths were as wide as 14.8 GHz, with thicknesses in the range of 1.5–6.0 mm. In addition, such dual-region absorption performance was also observed in CNZF/GN nanocomposites with other compositions. The appearance of dual-region absorption and the mechanism of microwave absorption were discussed in detail. It is expected that this CNZF/GN nanocomposite can be used as a new type of an efficient microwave absorber with light weight.

Facile Synthesis and Hierarchical Assembly of Flowerlike NiO Structures with Enhanced Dielectric and Microwave Absorption Properties

In this work, two novel flowerlike NiO hierarchical structures, rose-flower (S1) and silk-flower (S2), were synthesized by using a facial hydrothermal method, coupled with subsequent postannealing process. Structures, morphologies, and magnetic and electromagnetic properties of two NiO structures have been systematically investigated. SEM and TEM results suggested that S1 had a hierarchical rose-flower architecture with diameters in the range of 4-7 μm, whereas S2 exhibited a porous silk-flower architecture with diameters of 0.7-1.0 μm. Electromagnetic performances indicated that the NiO hierarchical structures played a crucial role in determining their dielectric behavior and impedance matching characteristic, which further influenced the microwave attenuation property of absorbers based on them. Due to its hierarchical and porous architectures, S2 had higher microwave absorption performances than S1. The maximum RL value for sample S2 can reach -65.1 dB at 13.9 GHz, while an efficient bandwidth of 3 GHz was obtained. In addition, the mechanism of the improved microwave absorption were discussed in detail. It is expected that our NiO hierarchical structures synthesized in this work could be used as a reference to design novel microwave absorption materials.

Mechanical, thermal and dielectric properties of graphene oxide/polyimide resin composite:

Graphene oxide (GO) sheets have captured the attention of the scientific community because of its excellent performance and applicability. Hence, studying its reinforcing effects on polyimide (PI) resin is an important research topic. In this study, samples of GO-reinforced PI resin were prepared by hot pressing. The effects of GO as nanofiller on the structure and morphology as well as on the mechanical, thermal, and dielectric properties of the GO/PI resin composites were investigated carefully to provide a practical strategy for the use of the polymer-based composites. The GO nanosheets were dispersed uniformly into the PI matrix by ultrasonication, as illustrated by scanning electron microscopic images (SEM). Compared with pure PI, the GO/PI resin composite loaded with 1 wt% GO showed improved tensile strength by 38.9%, flexural strength by 24.8%, and impact strength by 40.7%. Dynamic mechanical analysis test showed that the addition of GO (1 wt%) increased the glass transition temperature by nearly 9.1°C. In addition, the thermal stability and the dielectric constant were also enhanced by adding only a small amount of GO. This approach provides a strategy for developing simple and cost-effective GO-polymer resin composite materials.

Preparation and characterization of a novel composite of polythioetherimide/bismaleimide/2,2′-diallylbisphenol A

A novel composite of polythioetherimide (PTEI)/bismaleimide (BMI)/2,2′-diallylbisphenol A (BA) was prepared. Mechanical measurements, dynamic thermomechanical analysis, and microanalysis were conducted to assess the toughness and morphology of the composite. Results demonstrate that the addition of PTEI has significant effects on the mechanical properties of the BMI/BA system. Compared with the BMI/BA resin, the PTEI/BMI/BA system significantly improves the impact strength and bending strength, given an appropriate amount of PTEI. Scanning electron microscope (SEM) images and energy dispersive spectroscopy results show that PTEI is distributed uniformly in the PTEI/BMI/BA system and that the interfacial compatibility between the PTEI and BMI/BA phase is excellent. Thermogravimetric and dielectric analyses were also conducted to infer the thermal and dielectric properties of the composite. With a suitable addition of PTEI, the BMI/BA resin still exhibits good thermal resistance and dielectric constant and loss values of the blends still retain good stability in a frequency band from 10 MHz to 60 MHz. All these changes in properties are closely correlated with the addition of PTEI.

Mechanical and acoustical properties of polylactic acid based multilayer-structured foam biocomposites

Polylactic acid (PLA) based multilayer-structured foam biocomposites were prepared in a three-step process. In step 1, PLA plastic particles mixed with hollow glass beads (HGB) and other additives were blended, pelletized, and foamed and turned into plies using compression moldings. During step 2, the plies were stacked alternately and glued together with glass-fiber cloth reinforced PLA interlayers. The result is a multilayer-structured ply. In step 3, environmental sound-absorbing cotton was spliced on both sides of the ply to obtain the desired foam biocomposites. Then, foam morphology, and both mechanical and acoustical properties of the plies were investigated using a scanning electron microscope, a universal testing machine and a multianalyzer system. Our experimental results indicate that the compressive strength and acoustical properties of the plies made during the first step perform best when the mass fraction of HGB is 15%. We then compared a ply made in the first step with the multilayer-structured ply made in the second step. We found that the mechanical and sound insulation properties became more uniform after the addition of a PLA layer. We also found that the sound-absorbing cotton improved sound insulation by about 30%. The biocomposites achieved the best mechanical and acoustical properties after careful consideration of several factors.

The effect of polymerization temperature and reaction time on microwave absorption properties of Co-doped ZnNi ferrite/polyaniline composites

This study presents the systematic potential effects of reaction parameters on the synthesis of Co-doped ZnNi ferrite/polyaniline composites prepared via novel interfacial polymerization. Through intensive experiments and analysis, optimum reaction conditions including the polymerization temperature and reaction time are proposed so that the performance of the material is significantly improved. The structure, functional groups and morphologies of composites are investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). In addition, the electromagnetic properties and microwave absorption properties of Co-doped ZnNi ferrite/polyaniline composites are examined by a vibrating sample magnetometer (VSM), Quantum Design (MPMS-VSM and MPMS-XL), the superconducting quantum interference device (SQUID) magnetometer and vector network analysis. Based on these analyses, it is found that by tuning the reaction conditions, i.e., polymerization temperature and reaction time, microwave absorption capabilities in terms of the maximum reflection loss (RL) value and absorber thickness can be readily optimized. The results show that the composite with an optimized polymerization condition of 20 °C for 12 h displays remarkable microwave absorption properties with maximum reflectivity of −54.3 dB, and the effective bandwidth (RL < −10 dB) is about 6.02 GHz at a thickness of 6.8 mm. Furthermore, the discussion shows that the promising microwave absorption may be due to the uniform urchin-like structure of the composites.

Transmittance enhancement of micro-grating structure sapphire with high-refractive index Y2O3 layer

Abstract The theoretical analysis of micro-grating structure sapphire (sapphire MGS) with Y2O3 layer using the finite-difference time-domain method is presented. The results show that the total transmittance and reflectance of Y2O3/sapphire MGS have a close relationship with the thickness of Y2O3 layer, where about 300 nm is the ideal thickness. According to the simulant results, 300 and 600 nm of thicknesses of Y2O3 layer deposited onto sapphire MGS substrate by reactive magnetron sputtering method are studied experimentally. The experimental results agree well with the calculated data and further have better optical properties because of the rough surface of Y2O3 layer. It illustrates that the 300-nm Y2O3/sapphire MGS exhibits the best increase in the total transmittance and diffuse transmittance due to the greater graded refractive index profile than sapphire MGS. The results of this paper have potential applications in solar cells and diffraction grating.

Preparation and characterization of a novel benzoxazines/bismaleimide/2,2′-diallylbisphenol A blend with multiphase structures:

Novel benzoxazine (BOZ)/bismaleimide (BMI)/2,2′-diallylbisphenol A (BA), with a multiphase structure, was successfully prepared under the catalysis of methyl p-toluenesulfonate (PTSM) through reaction-induced phase separation. The curing reaction of BOZ with BMI and ring-opening polymerization of BOZ under the catalysis of PTSM were studied by Fourier transform-infrared spectroscopy and differential scanning calorimetry analyses, respectively. Mechanical measurements, thermogravimetric analysis, and microanalyses were conducted to assess the toughness and morphology of the composite. The reaction between BOZ and 4,4′-bismaleimidodiphenyl methane (BDM) occurs at a relatively high temperature. The ring-opening reaction of BOZ starts at a low temperature of 100°C because of the catalysis of PTSM. The BOZ/BDM/BA system with an appropriate amount of BOZ significantly improves the impact strength and flexural strength compared with those of the BA/BDM resin. The BOZ/BDM/BA system with PTSM also features high impact strength and flexural strength. Scanning electron microscopy images and energy-dispersive spectroscopy results show that BOZ-rich phase is dispersed in BDM-rich phase in the BOZ/BDM/BA system with PTSM. Thermogravimetric data show that the BOZ/BDM/BA blend with a multiphase structure exhibits superior thermal resistance to those of the BOZ/BDM/BA and BA/BDM resins. The formation mechanism of the ternary system under the catalysis of PTSM is elucidated with Gibbs free energy theory.

Microstructure, Mechanical and Thermal Properties of Three-dimensional Braided Glass Fiber Reinforced Phenolic Cryogel Composites

Phenolic cryogel plates (PCPs) and three-dimensional braided glass fiber reinforced phenolic cryogel composite plates (PCCPs) were successfully fabricated by microemulsion-templated sol gel polymerization and freeze-drying methods. Then, pore morphology, mechanical and thermal properties of the composites were investigated. The experimental results showed that the aerogels made by freeze-drying method had the best microstructure. In addition, it was discovered that the compressive and tensile strength of the cryogel plates had equally increased for approximately 8 and 30 times after compounding with glass fiber. Simultaneously, the mechanical properties of the 20 wt% and 25% solid content (PCPs) achieved the optimal value compared with PCPs of other contents. Moreover, it was found that the cryogels had excellent thermostability, and their thermal conductivity decreased with the reducing of the solid contents, whats more, the joining of glass fiber had the increased the composites’ thermal conductivity to some degree. Finally, considering the requirement of low density, good mechanical and thermal performance, the 20 wt% solid content PCCP had the best comprehensive performance compared with others.