Preparation of stable slurries of spherically shaped silica for coatings

In the past, the use of nanoparticles has been a subject of intensive research both in the academic world and industry. Amorphous silica has proven to be a material of choice for coatings to improve properties such as scratch resistance. The silica used in this paper consists of spherically shaped particles with median diameters of 130 and 180 nm and purities of 99.9 and 97.0%, respectively. Due to their size between nano and micro-particles, dispersion problems are less and properties inherent to nanoparticles are achieved. The preparation of stable water and hydrocarbon (D60) slurries is investigated in this article.Different types of commercial additives were used, and their effects on agglomerate size, zeta-potential and rheology of the dispersions were investigated. The experimental results are in good agreement with the DLVO theory. In water, the pH and the purity of the silica were critical parameters to achieve a stable slurry. Difficulties related to trace impurities can be overcome by using suitable additives and equipment. In the case of the hydrocarbon matrix, the critical factor to achieve a slurry having sufficient solids content and good rheological properties was the length of the hydrocarbon chain of the stabilizing additives.The benefits of adding these types of silica in solvent-borne, water-borne, and UV-cured coatings were investigated in a previous article (Lamy et al. [1]).