Aerogel, also known as dry gel. When most of the solvent is removed from the gel, the liquid content in the gel is much less than the solid content, or the medium filled in the spatial network structure of the gel is gas, and the appearance is solid, this is called dry gel, also known as aero gel. Such as gelatin, arabic gum, silicone, hair, nails, etc. Aerogel also has the properties of gel, that is, expansion, thixotropy and desizing. 
Aerogel is a kind of solid material form, one of the small density solids in the world. The density is 3 kilograms per cubic meter. The common aerogel is silicon aerogel gel, which was first made by American scientist Kistler in 1931 for gambling with his friends. There are many kinds of aerogels, including silicon, carbon, sulfur, metal oxide, metal and so on. Aerogel is a compound word. Here aero is an adjective, which means flying. Gel is obviously gel. It literally means a flying gel. The gel of any substance can be called aerogel as long as it can be dried to remove the internal solvent and keep its shape basically unchanged, and the product has high porosity and low density. 
Because of its extremely low density, the lightest aerogel at present is only 0.16 mg/cm3, slightly lower than the air density, so it is also called "frozen smoke" or "blue smoke". Due to the extremely small particles inside (at the nanometer level), visible light scatters less when passing through it (Rayleigh scattering), just like sunlight passing through air. Therefore, it also appears blue like the sky (if nothing else is mixed in), and slightly red when viewed in front of light. The sky is blue, while the evening sky is red. Since more than 80% of the aerogel is air, it has a very good heat insulation effect. An inch thick aerogel is equivalent to 20 to 30 pieces of ordinary glass. Even if the aerogel is placed between the rose and the flame, the rose will not be damaged at all. 
Aerogel also has a variety of uses in space exploration, including the Russian "Peace" space station and the American "Mars Pathfinder" probes. Aerogels are also used as detectors of the Cherenkov effect in particle physics experiments. A particle discriminator called Aerogel Cherenkov Counter (ACC) in the Belle experimental detector of B meson factory, a high-energy accelerator research institution, is a recent application example. The aerogel used in this detector has the characteristics of low refractive index between liquid and gas, as well as high transmittance and solid state, which is superior to the traditional method of using cryogenic liquid or high-pressure air. Meanwhile, its lightweight nature is also one of its advantages. 
Aerogel was originally named by S. Kistler. Because he successfully prepared silica aerogel by supercritical drying method, aerogel is defined as the material obtained by supercritical drying of wet gel, called aerogel. In the middle and late 1990s, with the emergence and development of atmospheric pressure drying technology, the generally accepted definition of aerogel in the middle and late 1990s is that no matter what drying method is used, as long as the liquid in the wet gel is replaced by gas, and the network structure of the gel is basically unchanged, the materials thus obtained are called aerogels. The structural feature of aerogel is a cylindrical multi branched nano porous three position network structure with high permeability, high porosity, low density, high specific surface area, and ultra-high pore volume ratio. Its bulk density is adjustable in the range of 0.003-0.500 g/cm-3. The density of air is 0.00129 g/cm3.
The preparation of aerogels usually consists of sol gel process and supercritical drying treatment. In the process of sol gel, by controlling the hydrolysis and polycondensation reaction conditions of the solution, nano clusters with different structures are formed in the solution, and the clusters adhere to each other to form a gel, while the solid skeleton of the gel is filled with liquid reagents left after the chemical reaction. In order to prevent the damage of the material structure caused by the surface tension in the micropore during the drying process of gel, the supercritical drying process is used to treat the gel. The gel is placed in a pressure vessel for heating and boosting, so that the liquid in the gel will become a supercritical fluid, the gas-liquid interface disappears, and the surface tension no longer exists. At this time, the supercritical fluid is released from the pressure vessel, and the porous, disordered, low-density aerogel material with a nanoscale continuous network structure can be obtained. 
An ultra light aerogel gel has been prepared by the research group of Gao Chao, professor of the Department of Polymer Science, Zhejiang University. It has broken the record for the lightest material in the world, with high elasticity and strong oil absorption capacity. The density of this solid material, called "all carbon aerogel", is 0.16 mg per cubic centimeter (the density of air thrown out), which is only 1/6 of the air density. According to experts, aerogel is the lightest material in the Guinness World Record. It is named because it has many pores and is full of air. 
In 1931, American scientists made the earliest aerogel with silicon dioxide, nicknamed "solidified smoke". In 2011, the HRL laboratory of the "carbon sponge" (3 pieces) with an area of about 8 cubic centimeters in the United States, the University of California Irvine and the California Institute of Technology jointly prepared an aerogel composed of nickel, with a density of 0.9 mg/cubic centimeter, setting the record for the lightest material at that time. Place this material on dandelion flowers, and the soft fluff will hardly deform. China has abundant graphite reserves, accounting for two-thirds of the world's total. 
Scientific researchers have been exploring methods for efficient utilization of graphite. Transforming graphite into graphene (a single-layer sheet-like structure composed of carbon atoms) can increase its value thousands of times. After five or six years of exploration, the advanced research team has prepared one-dimensional graphene fibers and two-dimensional graphene films. I plan to make graphene into a three-dimensional porous material to break the record set by American scientists.