The effect of silica thickness on nano TiO₂ particles for functional polyurethane nanocomposites

In order to help reduce the agglomeration of TiO₂ nanoparticles in polyurethane coatings while enhancing their photoactivity and mechanical/physical properties, this work examined encapsulating TiO₂ nanoparticles in a thin layer of SiO₂, prior to their nanocomposite polymerization. By applying a Stöber process, varying thicknesses of SiO₂ were successfully coated onto the surface of anatase and rutile TiO₂ nanoparticles. The methylene blue results showed that different loadings of SiO₂ onto the TiO₂ surface significantly influenced their photocatalytic activity. When the loading weight of SiO₂ was lower than 3.25 wt%, the photocatalytic activity was enhanced, while with higher loadings, it gave lower photocatalytic activity. When the rutile phase TiO₂ surface was fully covered with SiO₂, an enhanced photocatalytic activity was observed. When these silica coated nanoparticles were applied in polyurethane coatings, increasing the amount of SiO₂ on the titania surface increased the coatings contact angle from 75° to 87° for anatase phase and 70°-78° for rutile phase. The Young's modulus was also increased from 1.06 GPa to 2.77 GMPa for anatase phase and 1.06-2.17 GPa for rutile phase, attributed to the silica layer giving better integration. The thermal conductivity of the polyurethane coatings was also successfully decreased by encapsulating SiO₂ on the titania surface for next generation high performance coatings.