In 1931, Kistler prepared the world's first aerogel. He dried the gel (similar to jelly, consisting of a solid network skeleton and the liquid contained in the network) in supercritical technology, replacing the liquid in the gel with air, while keeping the solid network structure in the gel from collapsing, that is, the aerogel. In contrast, if the gel is dried directly, the capillary force caused by the evaporation of the liquid in the network usually causes the network to shrink, resulting in a dense rather than porous material. This unique porous and loose structure gives aerogel very low density, as well as very low thermal conductivity and large specific surface area. Due to these excellent properties, aerogels are expected to be "miracle materials that change the world", and are used as thermal insulation materials, sound insulation materials, optical materials, catalyst carriers, etc., and have important application prospects in chemistry, optics, electricity, aerospace, life sciences and other fields.
      In the early stage, the network skeleton of aerogel was mainly composed of inorganic materials such as nano-scale silica. The high porosity of aerogel made the skeleton very brittle and poor durability in practical application environment. The supercritical drying technology used is complicated in steps, high in cost and limited in size. Therefore, it is the goal of researchers to prepare aerogel with excellent mechanical properties by an economical and convenient method.
      Introducing organic components into silica aerogel is an effective way to improve the brittleness of traditional inorganic aerogel. The prepared organic-inorganic hybrid aerogel can obtain good flexibility due to the intervention of organic components. A representative work is the organic-inorganic hybrid molecule containing thioether chain segment prepared by researchers Ning Zhao and Jian Xu of the Institute of Chemistry of the Chinese Academy of Sciences through molecular design. The two ends of this molecule are trialkoxy silicon, which is hydrolyzed and condensed to produce a skeleton similar to silica gel, and the flexible thioether chain segment in the middle can give the gel skeleton flexibility. The gel can be vacuum dried directly at room temperature to obtain aerogel, greatly simplifying the preparation process. The obtained aerogel not only retains the original size of wet gel completely, but also has the advantages of low density, low thermal conductivity and high specific surface area.

      The results show that the flexible thioether segment enables the gel skeleton to withstand the compression of capillary force by changing its conformation during solvent volatilization under vacuum, and its lower polarity also helps to weaken the interaction between the gel and the solvent. The rapid evaporation of solvent also shortens the acting time of capillary force and reduces the damage effect of stress accumulation on gel skeleton structure. At the same time, the rapid evaporation of the solvent takes away a lot of heat, the temperature of the system decreases rapidly, the reactivity of the silicon hydroxyl group is reduced, and the generation of irreversible deformation is reduced, which is very favorable for maintaining the structure of the gel. Compared with the traditional silica aerogel, the new aerogel shows excellent flexibility and elasticity, can maintain the structure at 50% deformation, and can be repeatedly compressed at 30% deformation after many times quickly rebound without permanent deformation. This is the first report on the preparation of aerogel materials by vacuum drying technology in the world.
      As research has developed, the definition of aerogel has also changed. Initially, the material obtained from the wet gel by special supercritical drying was called aerogel. With the development of drying method and aerogel preparation technology, light porous materials with complete structure can also be obtained by freeze-drying, atmospheric pressure drying, vacuum drying and other technologies. In 1998, Husing and Schubert et al. proposed that the porous materials in which the gel network and pore structure of the wet gel can be largely retained after drying are called aerogels, and this definition focuses more on the structural characteristics of the aerogel material itself. With the development of other new aerogels, the definition of aerogels has been modified, and it is considered that the material with zero-dimensional, one-dimensional or two-dimensional material as the dispersive phase sol system, obtained by continuous or discontinuous gelation, and then dried to obtain a highly maintained gel network and pore structure is an aerogel.
    At present, a variety of aerogel materials have been developed, including organic or inorganic, or organic inorganic hybrid, soft or hard, conductive or insulating, transparent or opaque, and so on, this novel material will be more widely used.