In materials science, the “lightness” of a material is quantified by density, which measures a substance’s mass per unit volume. Materials engineered for extreme lightness achieve incredibly low densities by structuring their solid components to contain vast amounts of air. This pursuit leads to the creation of synthetic materials that challenge the limits of what a solid substance can be, effectively turning air into a structural component. The progression toward lighter and lighter solids represents an ongoing scientific endeavor, constantly pushing the boundary of low-density engineering.
The Current Record Holder
The current title for the world’s lightest solid material is held by a substance known as Graphene Aerogel, sometimes referred to as Aerographene. This material has achieved a confirmed density as low as approximately \(0.16 \text{ milligrams per cubic centimeter } (\text{mg/cm}^3)\). For perspective, the density of air at standard temperature and pressure is around \(1.2 \text{ mg/cm}^3\), meaning this solid is about seven and a half times less dense than the air surrounding it.
Graphene Aerogel is a form of aerogel, utilizing graphene, a single-atom-thick sheet of carbon, as its structural backbone. This ultralow density dethroned the previous record holder, Aerographite, a carbon-based foam developed in 2012, which had a slightly higher density of about \(0.18 \text{ mg/cm}^3\). Before these carbon structures, silica aerogel, invented in the 1930s, was the primary contender. The consistent reduction in density reflects the sophistication of modern nanomaterial engineering.
The Science Behind Ultralight Structures
The secret to Graphene Aerogel’s exceptional lightness lies in its intricate, self-supported three-dimensional nanoporous architecture. The material is primarily composed of air, with the solid component making up less than \(0.01\) percent of the total volume. This structure is created by taking a precursor solution, typically graphene oxide, and forming a hydrogel, which is then dried using specialized processes like freeze-drying or supercritical drying.
This specialized drying method removes the liquid without allowing the internal solid network to collapse, which is what happens during normal evaporation. The resulting solid matrix is an interconnected, honeycomb-like network of covalently bonded carbon sheets surrounding vast pockets of air. The incredibly high porosity means the material’s mass is distributed across a massive surface area.
The material’s strength, despite its low density, is derived from the robust nature of the graphene sheets and the way they are linked together. This design principle allows the aerogel to be compressed significantly—in some cases, past \(50\) percent of its volume—and still recover its original shape. The engineering goal is to maximize the void space while maintaining the mechanical integrity of the tiny remaining solid structure.
Practical Uses and Potential Applications
The unique combination of ultralow density, high porosity, and large surface area in Graphene Aerogel translates into a wide array of technological applications. One immediate use is in environmental remediation, particularly in cleaning up oil spills. The aerogel can absorb organic pollutants, like oil, up to \(900\) times its own weight, making it an extremely efficient sponge for cleanup efforts.
In the field of energy storage, the material’s high electrical conductivity and porous structure make it an excellent candidate for electrodes in advanced batteries and supercapacitors. The large internal surface area allows for maximum contact between the electrode material and the electrolyte, which can significantly enhance charging and discharging rates. Its light weight also makes it desirable for portable electronics and electric vehicles.
The aerogel is a superior thermal insulator, even surpassing traditional silica aerogels, because the tiny air pockets restrict the movement of gas molecules, inhibiting heat transfer. This property is leveraged in specialized insulation for high-performance gear and aerospace applications, such as insulating spacecraft and Mars rovers. Furthermore, the material’s structural properties, being stronger than steel for its weight, position it for use in lightweight structural components in the aerospace industry.