LAUSR

DOI: 10.1002/admi.201900314 properties. However, most synthesis methods usually involve chemical reactions in gel preparation and are limited to specific materials. In addition, the manufacturing cost introduced by delicate processes such as supercritical drying in preparing high-quality aerogels requires high pressure equipment and consumes large amount of liquid carbon dioxide can pose challenge for large scale deployment. Here, we develop a facile approach to prepare monolithic polymer aerogel based on poly(vinyl chloride) (PVC) via physical processes at ambient environment. Instead of making porous network via crosslink between different molecular chains or covalent bonding between diffe rent nanoparticles,[8,17] the porous network is formed by polymer chains entanglement between different precipitated polymer clusters. Taking advantage of the flexibility of polymer, the porous network remains robust while drying at ambient environment and shows a very low thermal conductivity approaching the air conductivity. Combing with the porosity and pressure dependent thermal conductivity, the thermal transport mechanism in PVC aerogel is carefully analyzed. Furthermore, superhydrophobicity is observed in these synthesized high porosity PVC aerogels. We developed an ambient synthesis process of PVC aerogel mainly consisting of three steps: gelation, solvent exchange, and drying (Figure 1a). First, the reaction sources, i.e., PVC powder (389 293, Sigma-Aldrich, USA) is mixed with dimethylformamide (DMF) (DX1727, EMD Millipore, Germany) with ratio from 0.2 g/10 mL to 1 g/10 mL at temperature of 60 °C. The porosity of aerogel is controlled by tuning the concentrations of PVC solutions. Second, the solution is sonicated for an hour and exposed to air for 12 h, from which the water vapor is absorbed into DMF/PVC solution. Consequently, the solubility of PVC decreases gradually resulting in the precipitation of polymer particles. Finally, a white and jelly-liked PVC solid was formed. To remove the liquid from the PVC gel while avoiding shrinkage of the porous structure, the solvent is exchanged with ethanol, which has a small surface tension. The solvent exchange process includes five steps each with a time interval of 6 h to gradually increase the volume percentage of ethanol in the solvent from 0%, 25%, 50%, 75%, 87.5% to 93.8%. High performance thermal insulation materials are desired for a wide range of applications in space, buildings, energy, and environments. Here, a facile ambient processing approach is reported to synthesize a highly insulating and flexible monolithic poly(vinyl chloride) aerogel. The thermal conductivity is measured respectively as 28 mW (m K)−1 at atmosphere approaching the air conductivity and 7.7 mW (m K)−1 under mild evacuation condition. Thermal modeling is performed to understand the thermal conductivity contributions from different heat transport pathways in air and solid. The analysis based on the Knudsen effect and scattering mean free paths shows that the thermal insulation performance can be further improved through the optimization of porous structures to confine the movement of air molecules. Additionally, the prepared aerogels show superhydrophobicity due to the highly porous structures, which enables new opportunities for surface engineering. Together, the study demonstrates an energy-saving and scalable ambient-processing pathway to achieve ultralight, flexible, and superhydrophobic poly(vinyl chloride) aerogel for thermal insulation applications.