The extraordinarily low density and hyper-high specific surface area of aerogels rely entirely on their nanostructured, three-dimensional porous networks. However, converting liquid precursors into such fragile solid materials has historically posed one of the most complex chemical and engineering challenges in modern industry. The evolution of aerogel processing is essentially a masterclass in removing liquid phases without collapsing the delicate underlying nanoscale architecture.

The primary phase of aerogel fabrication begins with the Sol-Gel process. During this stage, precursor molecules (such as alkoxysilanes, organic monomers, or metal salts) undergo hydrolysis and polycondensation within a solvent medium to form a suspension of nanoparticles (the sol). As reactions progress, these nanoparticles cross-link to form an interconnected liquid-filled network extending throughout the container (the gel). Precise control of reaction kinetics—including pH, temperature, catalyst selection, and solvent ratios—directly dictates the pore size distribution and mechanical strength of the resulting skeleton.

Nonetheless, the most critical and technologically demanding phase is the drying stage. If traditional thermal evaporation drying is employed, the liquid evaporating within the narrow nanopores exerts massive capillary forces. These forces instantaneously crush the fragile nanonetwork, causing the material to shrink densely into a conventional xerogel. To bypass this barrier, Supercritical Drying (SCD) technology was developed.

The core physics of supercritical drying hinges on the properties of substances at their thermodynamic critical point. When a solvent exceeds its critical temperature and critical pressure, the phase boundary between gas and liquid disappears, reducing surface tension to absolute zero. By slowly releasing the supercritical fluid, the liquid contained within the gel pores can be completely extracted without inducing capillary stress, thereby preserving the intricate three-dimensional nanonetwork intact. Supercritical carbon dioxide (sc-CO₂) extraction remains the gold standard in industrial processing due to its lower operating temperatures, environmental safety, and chemical stability.

In recent years, material scientists have focused on overcoming the high costs and lengthy processing cycles of supercritical drying. Ambient Pressure Drying (APD) technology modifies the gel network's surface chemically (such as silanization/methylation) to introduce strongly hydrophobic groups. This induces a "spring-back effect," allowing the gel to recover its volume after temporary compression during ambient evaporation. The combination of ambient drying and continuous sol-gel processes is dramatically driving down manufacturing costs, accelerating the transition of aerogels from specialized aerospace applications into large-scale industrial markets.