Size selectivity during dip coating of sol–gel silica-based antireflective coatings and its effect on the porosity of the coatings

The behavior of the particle size distribution (PSD) during the preparation of sol–gel silica-based antireflective coatings (ARCs) by dip coating was examined. It was found that the PSD after deposition differs dramatically from the PSD in the sol–gel suspensions, with the PSD after deposition being much narrower. A correlation between a decrease in the porosity of the ARC and an increase in the dispersity of the deposited PSD was also found. Hence, controlling the PSD during deposition has a direct effect on the resulting porosity and thus on the reflectance of an ARC. It was found that the temperature and deposition speed during dip coating, respectively, have very little effect on the deposited PSD. It was found that the PSD of the sol–gel suspension control the content of the deposited PSD, but does not change the range of sizes deposited. Finally, it was found that random-uniform particle placement results in elongated sequences of four or more particles, which supports our previous conclusion that the linear permittivity mixing rule is most appropriate for Stöber-based ARCs.