Highly Deformable High-Strength SiO₂ Aerogel Designed with an Alternating Structure of Hard Cores and Flexible Chains for Thermal Insulation

Abstract

Thermally insulating aerogels can now be prepared from ceramics, polymers, carbon, and metals and composites between them. However, it is still a great challenge to make aerogels with high strength and excellent deformability. We propose a design concept of hard cores and flexible chains that alternately construct the aerogel skeleton structure. The approach gives the designed SiO 2 aerogel excellent compressive (fracture strain 83.32%), tensile. and shear deformabilities, corresponding to maximum strengths of 22.15, 1.18, and 1.45 MPa, respectively. Also, the SiO 2 aerogel can stably perform 100 load−unload cycles at a 70% large compression strain, demonstrating an excellent resilient compressibility. In addition, the low density of 0.226 g/cm 3 , the high porosity of 88.7%, and the average pore size of 45.36 nm effectively inhibit heat conduction and heat convection, giving the SiO 2 aerogel outstanding thermal insulation properties [0.02845 W/(m•K) at 25 °C and 0.04895 W/(m•K) at 300 °C], and the large number of hydrophobic groups itself also gives it excellent hydrophobicity and hydrophobic stability (hydrophobic angle of 158.4°and saturated mass moisture absorption rate of about 0.327%). The successful practice of this concept has provided different insights into the preparation of high-strength aerogels with high deformability.

SiO2 Nanostructure-Based Aerogels with High Strength and Deformability for Thermal Insulation

“…To meet the needs of a new generation of lightweight and high-strength materials, polyhedral oligomeric silsesquioxane (POSS), a polyhedral nanostructure hybrid system, was developed by the Technology Advancement Committee of the US Air Force Research Laboratory in the mid-1990s of the last century. − POSS has a hexahedral core formed by alternating Si–O bonds, which is the structural support that gives it high strength, and Si atoms at the eight top corners are connected to functionalized groups that exhibit different physicochemical properties. − Therefore, the SiO 2 aerogel prepared by using the Si–O–Si hexahedral cores in POSS as the strength support part and establishing a certain length of molecular chain between the cores for connection theoretically has high strength and excellent deformability, which are expected to overcome the poor mechanical properties. Based on this research idea, we used hexaphthalic acid as a flexible multilink molecular chain to connect the −Si–O–Si– hexahedral hard cores in the synthesized octa­(aminophenyl)-T8-POSS and successfully realized a special SiO 2 aerogel constructed alternately with −Si–O–Si– hard cores and double flexible chains.…”