Aerogel has been widely known as a low-density and highly porous material and is closely connected with the complex processing methods, such as freeze−drying or supercritical drying. In this work, using the polymerization-induced aramid nanofiber (PANF) as a building block, we put forward a modified freezing−drying method for the high-efficiency preparation of all-para-aromatic-amide aerogels. In the preparation process, PANF hydrogel is first frozen at −18 °C and then dried at 20−150 °C for the formation of PANF aerogel. The PANF framework formed during the freezing process is crucial for the formation of the PANF aerogel. Moreover, the space-occupying effect of ice crystals is also helpful for the formation of the macroscopic pore structure in the aerogel. Aerogels with large size or well-controlled shape could be successfully obtained by this method. Through the variation of PANF concentration in the hydrogel and drying temperature, aerogels with different densities (20−185 mg/cm 3 ) could be achieved, and the lowest density is reached at 150 °C, with the PANF concentration of 0.7%. The low-density PANF aerogels show high specific compressive strengths and low thermal conductivities, which are comparable to those resulting from the freeze−drying or supercritical drying method. Furthermore, the shrinkage phenomenon in the drying process could be skillfully utilized for the preparation of PANF aerogel-coated objects. The PANF aerogels could be applied as a thermal insulating material or shock absorption material in practical applications.

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This study presents a simple, inexpensive and environment-friendly fabrication strategy for microfluidic paperbased analytical devices which can resist the penetration of surfactant solutions and organic solvents, by using water-based polyurethane acrylate via UV light curing. The filter paper's barrier created using cured PUA could withstand surfactant solutions (10 wt%, CTAB, SDS and Triton X-100) and organic solvents (methanol, isopropanol, DMF, DMSO, etc). This is very useful for analyzing complicated biological samples on the microfluidic paper-based analytical devices. In addition, the expense of water-based polyurethane acrylate is very cheap (about $8/500 g) and PUA developer is water that is environmental-friendly. To further verify its advantage, we successfully demonstrated the proposed microfluidic devices for detection of E. coli targets in tap water and seawater via colorimetric analysis in a fast and convenient manner. Our results revealed that the linear response to E. coli BL21 was in the range of 10 4 ∼10 9 cfu/mL. The proposed method can effectively avoid the damage for the hydrophobic barriers from the solution even some aggressive liquids, and shows great potential in on-site analysis, environmental monitoring, and food safety.

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