A zirconium hybrid polyhedral oligomeric silsesquioxane derivative (Zr–POSS–bisDOPO) is synthesized by the corner-capping and Kabachnik–Fields reactions. It is characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR), and then used as a flame retardant in diglycidyl ether of bisphenol A (DGEBA) to endow epoxy resin (EP) with flame retardancy. The flame retardancy, thermal stability, and mechanical properties of the cured EP/Zr–POSS–bisDOPO composites are investigated. The results show that when Zr–POSS–bisDOPO is added by 5–7 wt%, the EP/Zr–POSS–bisDOPO composites pass the UL-94 V-0 rating test. In addition, they have a better flame-retardant effect than pure EP. The combination of Zr atom embedded in the Si O cubic cage and the two phosphaphenanthrene substituent groups in one corner of cubic cage is expected to realize the Zr/Si/P ternary intramolecular hybrid synergistic effect and achieve the possibility of dispersing metal–POSS cages at a sub-micrometer-scale level into polymer matrix. It also proves that Zr–POSS–bisDOPO produces phosphorus-containing free radicals and terminates the chain reactions in gas phase. Meanwhile the Si O Si and Zr O units are retained in the solid phase, which promote the char formation and enhance the flame retardancy. This kind of Zr-doped POSS will be helpful for developing the new metal–POSS hybrid flame-retardant and polymer composites. 相似文献
Self-healing hydrogels often possess poor mechanical properties which largely limits their applications in many fields. In this work, boron nitride nanosheets are introduced into a network of the poly(vinyl alcohol)/borax (PVA/borax) hydrogels to enhance the mechanical properties of the hydrogel without compromising the self-healing abilities. The obtained hydrogels exhibit excellent mechanical properties with a tensile strength of 0.410 ± 0.007 MPa, an elongation at break of 1712%, a Young's Modulus of 0.860 ± 0.023 MPa, and a toughness of 3.860 ± 0.075 MJ m−3. In addition, the self-healing efficiency of the hydrogels is higher than 90% within 10 min at room temperature. Benefiting from the excellent self-healing properties, the shapeability of the hydrogel fragments is observed using different molds. In addition, the hydrogels display rapid pH-driven shape memory effects and can recover to their original shape within 260 s. Overall, this work provides a new approach to hydrogels with integrated excellent mechanical properties, self-healing abilities, and rapid pH-driven shape memory effects. 相似文献
In order to meet the requirements of polymer dielectric materials for high thermal stability and excellent dielectric properties in the application of high-temperature film capacitors, a series of polyimide (PI) films are fabricated by introducing a self-synthesized aniline trimer (ACAT) with a conjugated structure in this work. Since the conjugated ACAT in the main chains of PI improves the electron polarization and carrier mobility of the PI molecular chains, the dielectric constant of the ACAT-PI films is greatly enhanced (4.4–7.4). Meanwhile, the dissipation factor does not increase apparently (0.002–0.013). The dielectric properties are stable even when the temperature is up to 200 °C, the thermal degradation temperature is as high as 450 °C, and the mechanical properties are also excellent (70–105 MPa). Among all the films, the PI film with 5 mol% ACAT exhibits the maximal energy density of 3.6 J cm−3 under the field of 426 kV mm−1, the high tensile strength (90 MPa) and the excellent thermal stability (Td5 = 515 °C). The work paves the way to prepare high-temperature polymer dielectric film materials with high energy storage density. 相似文献
The development of sensitive materials for standard and improvised explosives is greatly significant to homeland security. In this paper, the phosphotungstate (NaPT) doped polyphenylene vinylene (PPV) nanotube arrays (NTAs), with excellent optical response, chemical stability, and larger specific surface area, are successfully fabricated by means of the “precursor film” infiltration method. The efficient charge carriers' separation of PPV NTAs can be achieved by doping NaPT to realize the photoelectric detection of explosive vapors. In addition, the identification of six explosives, including ammonium nitrate (AN), dinitrotoluence (DNT), picric acid (PA), p-nitrotoluene (PNT), triacetone triperoxide (TATP), and trinitrotoluene (TNT), can also be realized through the fingerprint atlas. Moreover, the adsorption energy and excited oscillator intensity has also been employed to explain the interaction between NaPT doped PPV nanotube arrays and various explosive molecules. Obviously, the NaPT doped PPV developed has the potential to be used as an explosive sensor. 相似文献
Comparative experiments are performed in friction stir welding (FSW) of dissimilar Al/Mg alloys with and without assistance of ultrasonic vibration. Metallographic characterization of the welds at transverse cross sections reveals that ultrasonic vibration induces differences in plastic material flow in two conditions. In FSW, the plastic material in the peripheral area of shoulder-affected zone (SAZ) tends to flow downward because of the weakening of the driving force of the shoulder, and a plastic material insulation layer is formed at the SAZ edge. When ultrasonic vibration is exerted, the stirred zone is divided into the inner and outer shear layers, the downward material flow trend of the inner shear layer disappears and tends to flow upward, and the onion-ring structure caused by the swirl motion is avoided in the pin-affected zone. By improving the flow behavior of plastic materials in the stirred zone, ultrasonic vibration reduces the heat generation, accelerates the heat dissipation in nugget zone and changes the thermal cycles, thus inhibiting the formation of intermetallic compound layers.