Bicomponent composite fibers, due to their unique versatility, have attracted great attention in many fields, such as filtration, energy, and bioengineering. Herein, we efficiently fabricated polyvinylidene fluoride/polyimide (PVDF/PI) side-by-side bicomponent nanofibers based on electrospinning, which resulted in the synergism between PVDF and PI, and eventually obtained the effect of 1 + 1 > 2. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the morphology and chemical structure of nanofibers, indicating that a large number of side-by-side nanofibers were successfully prepared. Further, the thermal stability, mechanical strength, and filtration properties of PVDF/PI were carefully investigated. The results revealed that the bicomponent nanofibers possessed both good mechanical strength and remarkable thermal stability. Moreover, the mechanical properties of PVDF/ PI were strengthened by more than twice after the heat treatment (7.28 MPa at 25 °C, 15.49 MPa at 230 °C). Simultaneously, after the heat treatment at 230 °C for 30 min, the filtration efficiency of PVDF/PI membrane was maintained at about 95.45 ± 1.09%, and the pressure drop was relatively low. Therefore, the prepared PVDF/PI side-by-side bicomponent nanofibers have a favorable prospect of application in the field of medium- and high-temperature filtration, which further expands the application range of electrospun fiber membranes.
Transparent alumina with high transmission has been first successfully prepared by rapid vacuum pressureless sintering processing at lower sintering temperature and reduced soaking time, compared with conventional pressureless sintering. The alumina sintered at 1670°C for 5 min has a residual porosity of 0.002% and a real in-line transmission of 64% for a wavelength of 1100 nm. We show that soaking time has an effect on the densification and transparency of alumina sintered at 1650°C. With increasing sintering temperature and soaking time, densification and grain growth occurred, and above 20 min, grain size increases slowly. The real in-line transmission of alumina increased with the densification and decreased with pore size growth. The light transmission and absorption were greatly affected by the grain size and pore defects.
KMgBi single crystals are grown by using the Bi flux successfully. KMgBi shows semiconducting behavior with a metal-semiconductor transition at high temperature region and a resistivity plateau at low temperature region, suggesting KMgBi could be a topological insulator with a very small band gap. Moreover, KMgBi exhibits multiband feature with strong temperature dependence of carrier concentrations and mobilities.
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