The density g/cm3 of silica gel is a critical parameter for its use in various applications. This is because a high-density structure can improve its adsorption properties and thus its usefulness as a solvent.
Silica gel density varies among different types of silica. These include: granules, powders, and micropearls. The density is also dependent on the preparation process containing silicon source, gelling, aging, silylation, and drying; all of which can influence the hydrophobicity of the aerogel.
In general, a low-density silica structure has a larger pore size distribution and more connected pore morphologies than a high-density one. However, a large pore size can also cause difficulty for adsorption due to the high surface energy and the hydrophobicity of the silica aerogel.
These differences in water diffusion and pore connectivity are important because they determine the properties of the altered layer formed during silicate dissolution. In addition, they are relevant for understanding corrosion mechanisms and long-term residual dissolution behavior.
To identify the effect of structural differences on water diffusion and reactivity, two silica gel models were created using reactive force field-based molecular dynamics simulations. The first model used the original ISG composition that imparted a more interconnected glass network structure to the remnant silica gels, while the second simulated the hydrogarnet defect formation that created more isolated pores in the residual gel structures. These differences in the underlying network framework impacted the pore connectivity and nanoconfinement effects of the water molecules. These results highlight the complexity of the water network in silica gels and the importance of incorporating this information in modeling their diffusion and reactivity.