Zhenchao Qian

Robust Superhydrophobic Bridged Silsesquioxane Aerogels with Tunable Performances and Their Applications

Aerogels are a family of highly porous materials whose applications are commonly restricted by poor mechanical properties. Herein, thiol-ene chemistry is employed to synthesize a series of novel bridged silsesquioxane (BSQ) precursors with various alkoxy groups. On the basis of the different hydrolyzing rates of the methoxy and ethoxy groups, robust superhydrophobic BSQ aerogels with tailorable morphology and mechanical performances have been prepared. The flexible thioether bridge contributes to the robustness of the as-formed aerogels, and the property can be tuned on the basis of the distinct combinations of alkoxy groups with the density of the aerogels almost unchanged. To the best of our knowledge, the lowest density among the ambient pressure dried aerogels is obtained. Further, potential application of the aerogels for oil/water separation and acoustic materials has also been presented.

Fabrication of oriented hBN scaffolds for thermal interface materials

Thermal interface materials are widely used in thermal management, and usually require a high thermal conductivity, low coefficient of thermal expansion (CTE) and adequate softness. Herein, hBN/PDMS composites are fabricated by the infiltration of a PDMS prepolymer in the hBN scaffolds followed by a thermal curing process. The scaffolds are prepared by an ice templating method with hBN microplatelets, leading to a good alignment of hBN platelets along the z direction in the PDMS matrix. This unique structure results in a high thermal conductivity, which is about 3 times higher than that of the composites fabricated by a casting method, and the thermal conductivity is as high as 1.4 W m−1 K−1 along the z direction at ∼20 wt% of hBN microplatelets. The composites also possess low CTEs which are <100 ppm K−1 along the z direction and maintain an adequate softness.

Superelastic and ultralight polyimide aerogels as thermal insulators and particulate air filters

We utilized electrospun polyimide nanofibers as building blocks to construct a hierarchically porous architecture through freeze-drying. Superelasticity, recoverable ultimate strain of 99%, has been obtained by thermally induced intermolecular condensation. Aerogels also possess ultralow density, high-temperature stability, low thermal conductivity and excellent performance in PM2.5 filtration.

Aerogels Derived from Polymer Nanofibers and Their Applications

Aerogels are gels in which the solvent is supplanted by air while the pores and networks are largely maintained. Owing to their low bulk density, high porosity, and large specific surface area (SSA), aerogels are promising for many applications. Various inorganic aerogels, e.g., silica aerogels, are intensively studied. However, the mechanical brittleness of common inorganic aerogels has seriously restricted their applications. In the past decade, nanofibers have been developed as building blocks for the construction of aerogels to improve their mechanical property. Unlike traditional frameworks constructed by interconnected particles, nanofibers can form chemically cross-linked and/or physically entangled 3D skeletons, thus showing flexibility instead of brittleness. Therefore, excellent elasticity and toughness, ultralow density, high SSA, and tunable chemical composition can be expected for the polymer nanofiber-derived aerogels (PNAs). In this review, recent research progress in the fabrication, properties, and applications of PNAs is summarized. Various nanofibers, including nanocelluloses, nanochitins, and electrospun nanofibers are included, as well as carbon nanofibers from the corresponding organic precursors. Typical applications in supercapacitors, electrocatalysts for oxygen reduction reaction, flexible electrodes, oil absorbents, adsorbents, tissue engineering, stimuli-responsive materials, and catalyst carriers, are presented. Finally, the challenges and future development of PNAs are discussed.

Superhydrophobic/Superhydrophilic Janus Fabrics Reducing Blood Loss

Hemostatic fabrics are most commonly used in baseline emergency treatment; however, the unnecessary blood loss due to the excessive blood absorption by traditional superhydrophilic fabrics is overlooked. Herein, for the first time, superhydrophobic/superhydrophilic Janus fabrics (superhydrophobic on one side and superhydrophilic on the other) are proposed: the superhydrophilic part absorbs water in the blood to expedite the clotting while the superhydrophobic part prevents blood from further permeating. Compared with the common counterparts, effective bleeding control with reducing blood loss more than 50% can be achieved while the breathability largely remain by using Janus fabrics. The proposed prototypes can even prolong the survival time in the rat model with serious bleeding. This strategy for reducing blood loss via simply tuning wettability is promising for the practical applications.

Facile preparation of bridged silsesquioxane microspheres with interconnected multi-cavities and open holes

Creating hollow structures in microspheres is attracting increasing interest because of the notable large capacity, high porosity, low density and extended surface area of the hollow microspheres prepared. Herein, facile preparation of bridged silsesquioxane (BSQ) microspheres with interconnected multi-cavities and open-hole structures is presented. The well-developed multi-cavities are derived from the configuration of the water-in-oil-in-water emulsion of the precursor. The condensation of the precursor in the emulsion results in the transition of the liquid precursor to solid BSQ resin, which preserves the emulsion structure and induces the formation of voids. The resultant hollow BSQ microspheres show advantages in controllable cargo delivery.

Fire-Resistant, Ultralight, Superelastic and Thermal-Insulated Polybenzazole Aerogels

Efficient and durable thermal insulators combined with flame resistance are required for energy efficient buildings. Here, we fabricate poly(p-phenylene benzobisoxazole) (PBO) nanofiber aerogels (PBOAs) through a proton-consumption-induced gelation of PBO nanofiber sol and a controlled freeze-drying with a low cooling rate, followed by thermal cross-linking. Nanofibrous networks based on physical entanglement of nanofibers and chemical cross-linking at the junctions were obtained, leading to ultralow density (3.6–15.7 mg cm−3), high porosity (98.9–99.7%), high specific surface area (155.4 m2 g−1), low thermal conductivity (26.2–37.7 mW m−1 K−1) and superelasticity under an ultimate strain of 99%. More importantly, the aerogels achieve an excellent thermal stability, including a high decomposition temperature of 650 °C and a high long-term use temperature of 350 °C. Furthermore, the PBOAs are characterized by outstanding flame resistance, reach the nonflammable level in vertical burning tests (UL-94, V-0 class), and show a limiting oxygen index (LOI) as high as 52.8%. The aerogels cannot be ignited under simulated real-scale fire conditions, leaving suppressed smoke emission and reduced potential for flame spread and fire hazards. High thermal insulation and resistance to a 1000 °C flame has been achieved by compositing PBOAs with fumed silica. Thus, the PBOAs have promising applications in energy efficient areas, such as buildings, aerospace and many other fields, especially under harsh conditions.