Peijiang Liu

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.

Controllable synthesis and enhanced microwave absorption properties of silane-modified Ni0.4Zn0.4Co0.2Fe2O4 nanocomposites covered with reduced graphene oxide

For the first time, silane coupling agent modified Ni0.4Zn0.4Co0.2Fe2O4 ferrite covered with reduced graphene oxide nanocomposites were synthesized by a simple, efficient and controllable three-step method. The structural characteristics were investigated by Fourier transform infrared spectra, X-ray diffraction, elemental analysis, thermal gravity analysis, field-emission scanning electron microscopy and transmission electron microscopy. The results indicated that the coupling agent modified ferrite particles were firmly and uniformly covered on the rGO nanosheets. Microwave adsorption properties were also performed at room temperature in the frequency range of 2–18 GHz. The minimum reflection loss of rGO/APTS–NZCF composites can reach −51.8 dB at 15.1 GHz with the thickness of 2.1 mm, and the effective bandwidth corresponding to RL less than −10 dB was 5.3 GHz (from 12.7 to 18 GHz). The excellent microwave adsorption properties indicate this novel composite could be used as a new candidate for lightweight electromagnetic wave adsorption material.

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.

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.