Xuhai Xiong

Air@rGO€Fe3O4 microspheres with spongy shells: self-assembly and microwave absorption performance

Hollow reduced graphene oxide microspheres embedded with Fe3O4 (Air@rGO€Fe3O4) were synthesized by a water-in-oil (W/O) emulsion technique followed by a calcination process. Their multicomponent hierarchical 3D microstructure was confirmed by XRD, XPS, SEM and TEM analysis methods. These Air@rGO€Fe3O4 microspheres are of low density (0.85–0.95 g cm−3) and possess excellent microwave absorption properties and corrosion resistance. Their minimum reflection loss (RLmin) value reaches −52 dB at 10 GHz with a thickness of 2.8 mm, and the absorption bandwidth (lower than −10 dB) is 7.2 GHz covering from 7.5 GHz to 14.7 GHz. After treatment in hydrochloric acid for five days, Air@rGO€Fe3O4 microspheres still exhibit an impressive microwave absorption performance and the RLmin value reaches up to −46 dB at 8.6 GHz with an absorption bandwidth (lower than −10 dB) of 6.0 GHz (6.3–12.3 GHz) with a matching thickness of 3.5 mm. These results demonstrate that the Air@rGO€Fe3O4 microspheres may be attractive candidate materials for microwave absorption applications.

Synthesis, characterization, and curing kinetics of novel bismaleimide monomers containing fluorene cardo group and aryl ether linkage

Two novel bismaleimide (BMI) monomers containing fluorene cardo group and aryl ether linkage, that is, 9,9-bis[4-(4-maleimidophenoxy)phenyl] fluorene (PF-BMI) and 9,9-bis[4-(4-maleimidophenoxy)-3-methylphenyl] fluorene (MPF-BMI) based on 9,9-bis(4-hydroxyphenyl)fluorene and its derivative were designed and synthesized. The chemical structures of the monomers were confirmed from 1H NMR, 13C NMR spectroscopy, and Fourier transform infrared spectroscopy. Both monomers obtained are readily soluble in common organic solvents, such as acetone, dichloromethane, and chloroform, enabling an easy solution processing. The thermal curing behavior of the monomers and their non-isothermal thermal curing processes were investigated using differential scanning calorimetry, displaying that both monomers have lower melt points and broad thermal processing windows. The corresponding kinetic data, for example, activation energy (Ea), pre-exponential factor (A), and the order of the reaction (n), were obtained by the Kissinger and Ozawa method. The BMI resins based on these new monomers have good thermal stability seen from the thermogravimetric analysis results.

Self-assembly of ternary hollow microspheres with strong wideband microwave absorption and controllable microwave absorption properties

In this study, we report a simple and efficient two-step method consisting of water-in-oil (W/O) emulsion technique and subsequent annealing process for synthesizing the hollow reduced graphene oxide microspheres embedded with Co nanoparticles (Air@rGO€Co). The microspheres showed good electromagnetic properties because of the coexistence of magnetic loss and dielectric loss to microwaves. The minimum reflection loss (RLmin) value of S1.5 reaches −68.1 dB at 13.8 GHz with a thickness of 2.2 mm, and the absorption bandwidth (lower than −10 dB) is 7.1 GHz covering from 10.9 GHz to 18.0 GHz. More interestingly, we can easily controll the microwave absorbing properties of the microspheres by changing the ratio of the two components in the composites. The excellent electromagnetic match at the corresponding resonance peaks for dielectric and magnetic loss play an important role in improving microwave absorption property. Our study provides a good potential method for preparation of lightweight microwave absorbing materials.

Bismaleimide-diamine copolymers containing phthalide cardo structure and their modified BMI resins:

3,3-Bis[4-(4-aminophenoxy)phenyl]phthalide (PPDA) and 4,4′-bimaleimidodiphenyl-methane (BDM) were prepared via a Michael-type addition using molar ratio 1:2(PM2), 1:3(PM3) and 1:4(PM4) in acetone as solvent and acetic acid as a catalyst. The chemical structures of prepolymers were characterized by hydrogen-1 nuclear magnetic resonance (1H NMR) spectroscopy and Fourier transform infrared spectroscopy. These prepolymers exhibit good solubility in common organic solvents. The thermal properties of the prepolymers were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Composites composed of carbon cloth and the phthalide-containing Michael addition-type prepolymers (0.5% triphenylphosphine) were also prepared. The DMA results demonstrated that the resulting composites have excellent thermal stability. Besides, N,N-4,4′-bismaleimidodiphenylmethylene (BDM) and O,O′-diallyl bisphenol A (DABPA) resin blends were modified by PM2. We investigated the effects of mole concentration of prepolymers on the curing process, mechanical properties, fracture toughness, and heat resistance of the modified resins. The investigations of the mechanical properties showed a complicated trend with an increase in prepolymer contents. When the proportion of PM2 is 0.05, the impact strength of modified resins was increased by 121.3%. In addition, the moisture resistance of cured resins was improved with the increase in prepolymer contents.

Preparation and properties of bismaleimide resins based on novel bismaleimide monomer containing fluorene cardo structure

Novel bismaleimide resins based on 9,9-bis[4-(4-maleimidophenoxy)phenyl]fluorene (PFBMI), 2,2′-diallyl bisphenol A (DABPA), and 4,4′-dimaleimido diphenylmethane (BDM) were prepared in this article. The thermal properties of PFBMI/DABPA in different proportions (1:0.87, 1:1, and 1:1.2) were carefully characterized using differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The results showed that resins had good thermal stabilities especially the one at 1:0.87. Its 10% weight loss reached 433.4°C, and the residual weight percentage (RW%) was more than 50%. In addition, PFBMI was blended into BDM/DABPA in a different ratio, and the curing characteristic, thermomechanical behavior, thermal stability, mechanical properties, and moisture absorption behavior of these blends were investigated. The results revealed that the introduction of PFBMI into BDM/DABPA did not decrease the thermal stability of the modified resins but increased the RW% at 600°C. Moreover, the impact strength of the modified resins can be significantly enhanced; when the ratio is 0.08:1, it increased by 35%. The water absorption rate also decreased with the increase in the concentration of PFBMI. PFBMI monomers play an important role on the toughness reinforcement of the BDM/DABPA resin.

Synthesis and properties of bismaleimide resins containing phthalide cardo and cyano groups

Two novel n ≈ 1 oligomeric bismaleimide monomers containing phthalide cardo and cyano groups (PCBMI and MCBMI) were designed and synthesized. The chemical structures of the monomers were confirmed from proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. Both BMIs exhibit good solubility in common organic solvents, enabling easy solution processing. Thermal curing behaviors of the monomers were investigated by differential scanning calorimetry, displaying broad exothermic peaks and large thermal processing windows. Furthermore, PCBMI/carbon fiber composites were prepared, with their thermal stability and mechanical properties investigated. Thermogravimetric analysis and test of interlaminar shear strength indicated that the thermal polymerization of cyano groups improved the heat resistance of BMI resins and enhanced the interfacial adhesion at higher temperature.

The effects of thermally reversible agents on PVC stability properties

One kind of thermally reversible cross-linking agents for improving PVC thermally stability was synthesized. The chemical structure and thermally reversible characteristics of cross-linking agents were investigated by FTIR and DSC analysis, respectively. FTIR results confirmed that the cyclopentadienyl barium mercaptides ((CPD-C2H4S)2Ba) were successfully synthesized. DSC results showed it has thermally reversible characteristics and the depolymerization temperature was between 170 ?C and 205 ?C. The effects of cross-linking reaction time on gel content of Poly(vinyl chloride) compounds was evaluated. The gel content value arrived at 42% after being cross-linked for 25 min at 180 C. The static thermally stability measurement proved that the thermally stability of PVC compounds was improved.