[en] Graphical abstract: Upon AO exposure, pristine polyimide is severely eroded and exhibits linear degradation behavior, while HBPSi polyimides demonstrate high AO survivability. - Highlights: • Hyperbranched polysiloxane polyimides (HBPSi PIs) were fabricated by co-polymerizing HBPSi with imide monomers. • The degradation behavior of HBPSi PIs is assessed based on its evolution of surface chemistry and morphology. • There is a percolation threshold of HBPSi addition to achieve the most desirable atomic oxygen (AO) resistance. • Desirable AO resistance is associated with the rapid formation of a much denser and more connected silica passivating layer. • The silica passivating layer formed in situ is time-dependent and grows with AO fluence. - Abstract: Hyperbranched polysiloxane (HBPSi) polyimide membranes were fabricated by copolymerizing amine-functionalized HBPSi and imide monomers. The atomic oxygen (AO) resistance of the resulting polyimides were investigated in simulated AO environment, based on their evolution of surface chemistry and morphology. Results indicated that a silica passivating layer finally formed on the membrane surfaces and, there was a percolation threshold of HBPSi addition to achieve the most desirable AO resistance. This is explained by the formation of a much denser and more connected silica passivating layer in shorter time on the membrane surface at high HBPSi loading upon AO exposure

[en] BSA/Fe₃O₄ magnetic composite microspheres with high saturation magnetization and paramagnetic property were prepared via inverse emulsion technology at room temperature, bovine serum albumin (BSA, 60 KD), magnetic nanoparticles (Fe₃O₄) and glutaraldehyde as macromonomer, inorganic particles and cross-linking agent, respectively. Fourier transform infrared (FTIR), scanning electron microscope (SEM), metalloscope, and particle size analyzer were used to characterize morphology and structure of composite microspheres. Vibrating sample magnetometer (VSM) and thermogravimetric analysis (TGA) were used to test magnetic properties of the synthesized samples, adsorption capacity of microspheres was determined by ultraviolet spectrophotometer (UV). The results showed that BSA/Fe₃O₄ microspheres were 43 μm with relatively narrow particle size distribution, perfect sphere-shaped morphologies, superparamagnetism with a saturation magnetization of 11 emu/g, and high magnetic content with a value of 57.29%. The main factors influencing properties of microspheres including raw material ratio, the amount of emulsifier and cross-linking agent, agitation speed were investigated and optimized. Furthermore, these microspheres accompanying with high separable and reusable efficient may have great potential application in the field of separation, in particular, removal of antibiotics. Adsorption capacities of the microspheres of four different kinds of antibiotics (erythromycin, streptomycin, tetracycline and chloramphenicol) ranging from 69.35 mg/g to 147.83 mg/g were obtained, and Langmuir isotherm model coincided with equilibrium data than that of the Freundlich model. - Highlights: • BSA/Fe₃O₄ microspheres with high saturation magnetization were prepared. • BSA/Fe₃O₄ microspheres for the removal of antibiotics are proposed. • The obtained results have significant importance in environmental processes

[en] Polyimine vitrimers are a promising class of self-healing materials for their attractive dynamic reversible properties and ease of preparation without catalysts, but they still remain some challenges to overcome, such as poor mechanical properties and thermal stability or a higher temperature to reprocess and recycle. Herein, performance-modified polyimine vitrimers, combining flexibility, good mechanical properties and thermal stability with easy reprocessed/recycle properties, were studied by introducing aromatic diamines dimer (m-xylylenediamine dimer) into the polymer networks. The incorporation of m-xylylenediamine dimer increases the molecular chain of polymer networks, which makes the material more flexible and easy reprocessed. Besides, it owns two benzene rings and endows the dynamic polymer with broaden conjugation structure, which remains the material’s thermal stabilities and mechanical properties. Results show that the polymer material exhibits flexibility at room temperature [a glass transition temperature (T_g) of 72 °C, a storage modulus of = 1.56 GPa and stress at break of = 45 MPa (dry sample) and 27 MPa (wet sample)], possesses excellent thermal stability (a mass loss of 6.3% at 300 °C) and performs viscoelastic liquid behavior in very short relaxation times at lower temperatures (from 260 s at 70 °C to 22 s at 100 °C). In addition, the obtained networks could be more easily reprocessed and remolded in shorter times and at lower temperatures under the condition of heat, water and amine solvents without adding any catalyst.

[en] 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. .

[en] Highlights: • Janus polyimide films consisting of HBPSi enriched and scanty sides are fabricated. • The Janus structure is constructed by using the ‘twice-cast strategy’. • Janus polyimide films show both excellent AO resistance and mechanical properties. • Janus polyimide films demonstrate high optical transparency after AO exposure. Polyimide films are required onboard spacecrafts withstanding atomic oxygen (AO) erosion in low earth orbit environment. We report a janus polyimide composite film consisting of HBPSi enriched and scanty surfaces/sides. This unique structure ensures both outstanding AO resistance—with relative mass loss merely 8.34% that of standard Kapton H—and admirable mechanical performance with ultimate tensile strength as high as ca. 89 MPa and fracture toughness up to 5.22 MJ·m⁻³. Besides, janus polyimide composite films are good at maintaining its surface morphology and integrity upon AO attack, showing a higher transmittance after AO exposure (ca. 82% at 600 nm) and lower root mean square roughness (RMS) value (5.14 nm vs. 6.62 nm) in comparison to its monolayered counterpart. These janus polyimide films demonstrate exceptional performance and thus show great potential for making surface protective blanket for spacecrafts functioning in space environment.

[en] A growing number of core–shell structured microwave absorbents have been reported; nevertheless, there are few studies accessible about one-dimensional core–shell electromagnetic nanocomposites as microwave absorption materials. In this work, we have developed two kinds of novel electromagnetic nanocomposites, namely yolk–shell Fe₃O₄@void@SiO₂ nanochains and Fe₃O₄@void@SiO₂@PPy nanochains. Their components and morphologies have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectra, scanning electron microscope and transmission electron microscope. The N₂ adsorption–desorption isotherms have demonstrated their specific surface areas and porosity, and the magnetic properties have been recorded by the vibrating sample magnetometer. Investigation of microwave absorbing properties manifests that Fe₃O₄@void@SiO₂@PPy nanochains have stronger absorption capability and broader effective absorption bandwidth than Fe₃O₄@void@SiO₂ nanochains, which is caused by the introduction of polypyrrole shells, giving rise to the addition of conductive loss and the enhancement of dipole polarizations, interfacial polarizations, multiple reflection and absorption. Specifically, the minimum reflection loss value is − 54.2 dB (17.70 GHz) and the maximum effective absorption bandwidth can reach 5.90 GHz (11.49–17.39 GHz); thus, Fe₃O₄@void@SiO₂@PPy nanochains will become promising microwave absorption candidates. This research once more demonstrates that necklace-like core–shell magnetic–dielectric complex benefit to enhancement of microwave absorption performance, and establishes a good foundation for exploiting the high-effective microwave absorbing materials.