Polymer-based monolithic composite aerogels with a durable cross-linked structure were fabricated using polyvinyl alcohol (PVA) and para-aramid nanofibers (ANFs) as precursors, and supercritical fluid technology as a drying strategy. In order to give a clear insight into ANFs/PVA composite aerogels, we thoroughly investigated the influences of the molecular weights and dosage ratios of PVA on these composite aerogels, and clearly demonstrated the entire process of the evolution of "sol-gel-aerogel." The chemical composition, porous nanostructure, porosity, and mechanical performance of the ANFs/ PVA composite aerogels were characterized by attenuated total reflectance-Fourier transform-infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), nitrogen physical adsorption, and uniaxial compression, respectively. The results revealed the mechanism of the stable composition of ANFs/PVA binary system, and that both the molecular weights and dosage ratios of PVA in the ANFs/PVA composite aerogels have a significant influence on their properties. This work is beneficial to design and fabricate polymer-based aerogels with desirable chemical and physical characteristics, and the obtained ANFs/PVA composite aerogels with appropriate molecular weight and dosage ratio of PVA possess well-balanced comprehensive properties, which offer the potential for a wide range of applications.

Aerogels are frequently exposed to moisture or come into direct contact with water in real-world applications, posing a threat to their stable performance. Herein, based on the characteristic that the liquid phase can efficiently diffuse in the solid cross-linked network of gels, a robust hydrophobic modification approach for paraaramid nanofibers/polyvinyl alcohol (ANFs/PVA) composite aerogels with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) is demonstrated. The type of solvent, the concentration of hydrochloric acid (HCl) required promoting PFOTES hydrolysis, and the treatment time for hydrophobic modification are discussed individually. The ANFs/PVA/PFOTES aerogels with a water contact angle of 131.0 were obtained through supercritical fluid drying employing acetone as the solvent, with a concentration of 0.1 mol/L HCl of 0.35 vol%, and a treatment duration of 2 h. The hydrogen bond between ANFs and PVA, and the grafting of PFOTES on PVA have both been verified by Fourier-transform infrared spectroscopy. The porous structure of the modified aerogels was improved simultaneously, according to scanning electron microscope and Brunauer-Emmett-Teller characterizations.With the help of a thermal imaging camera, ANFs/PVA/PFOTES aerogels exhibit stable thermal insulation capability in low temperature and humid environments, which holds great promise for a wide range of applications.

Aerogels with porous nanostructures and extremely low densities have drawn a lot of interest recently due to their huge potential applications, but it remains a great challenge to construct tough aerogels with controllable structures. Herein, monolithic composite aerogels consisting of para-aramid nanofibers (ANFs) and cellulose acetate (CA) were successfully fabricated through the “sol–gel-aerogel” process and supercritical fluid drying. The possible presence of complex and strong hydrogen bonds between ANFs and CA was verified by attenuated total reflectance-Fourier transform infrared (ATR-FTIR). To provide a thorough understanding of ANFs/CA composite aerogels, we carefully analyzed their gelation process, macromorphology, micromorphology, porosity, mechanical property, and adsorption capacity. The results show that CA plays a key role in the structural enhancement, porous morphology adjustment, and additional functionalities of the ANFs/CA composite aerogels. ACA-2 exhibited balanced performance across all samples, which has a specific surface area of 315 m2/g, an average pore diameter of 8.53 nm, a pore volume of 0.671 m3/g, a bulk density of 0.0269 g/cm3, a porosity of 98.03%, and a compressive modulus of 1.208 MPa. This work will contribute to the design and production of polymer-based fibrous aerogels with ideal chemical and physical properties. ANFs/CA composite aerogels may have considerable application potential in the fields of filtration, adsorption, and drug delivery.

No abstract

AlN/Mo/Sc 0. 2 Al 0. 8 N composite structure films were prepared on Si (100) substrate by pulsed DC magne• tron sputtering， and the epitaxy of GaN films was grown by metal-organic chemical vapor deposition(MOCVD).Atomic force microscopy， high-resolution X-ray diffraction， powder X-ray diffraction， scanning electron microscopy and Raman spectroscopy were used to study the effect of the thickness of the Mo layer on the crystal quality of the Sc 0. 2 Al 0. 8 N layer and the GaN epitaxial layer， and the importance of the Sc 0. 2 Al 0. 8 N layer for the GaN epitaxial layer grown on Mo was also studied. The results show that the thickness of the Mo layer is an important factor affecting the Sc 0. 2 Al 0. 8 N layer and the GaN epitaxial layer， and the Sc 0. 2 Al 0. 8 N layer is of great significance to the epitaxy of GaN on Mo. When the thickness of the Mo layer is 400 nm， the crystal quality of the GaN epitaxial layer is the best， the