Why do silica sol manufacturers talk about the stability of silica sol?

Silica sol is a dispersion of nano silica particles, with a typical particle size of 3-150nm. The density of nano silica particles in silica sol is 2.2-2.3, while water has a density of 1, with a significant difference in density. However, we have observed that silica sol can remain suspended and stable for a long time. Why is this?

Ordinary silica sol is a water dispersed solution of nano silica, with negative charges on the surface of particles. Therefore, there is a repulsive effect of the same charge between particles, which prevents agglomeration. This is the fundamental reason for the stability of silica sol suspension system. In addition, the thermal motion of water molecules constantly impacts nanoparticles, causing them to be in motion (Brownian motion). Therefore, silica sol with small particle size can remain suspended and stable for a long time. For example, silica sol with particle size less than 50nm can be left to settle for a long time without particle settling; However, when the particle size of the silica sol is greater than 80nm, obvious particle settling can be observed after several months of standing. Precipitation can be observed at the bottom of the silica sol container, but this precipitation is a "soft precipitation". After stirring, it will be re dispersed evenly and restored to its original state. The reason why this "soft precipitation" can still be restored to a uniform liquid is because of the charge effect on the surface of the nanoparticles, and there is electrostatic repulsion between the particles.