Ultrasonic Dispersion of TiO ₂ Nanoparticles in Aqueous Suspension

Aggregation and dispersion behavior of nanometer and submicrometer scale TiO 2 particles in aqueous suspension were investigated using three kinds of mechanical dispersion methods: ultrasonic irradiation, milling with 5‐mm‐diameter balls, and milling with 50 μm beads. Polyacrylic acids with molecular weights ranging from 1200 to 30 000 g/mol were used as a dispersant, and the molecular weight for each dispersion condition was optimized. Viscosities and aggregate sizes of the submicrometer powder suspensions were not appreciably changed in the ultrasonic irradiation and 5‐mm‐ball milling trials. In contrast, in the trials in which nanoparticle suspension was used, ultrasonic irradiation produced better results than 5‐mm‐ball milling. Use of ultrasonication enabled dispersion of aggregates to primary particle sizes, which was determined based on the specific surface area of the starting TiO 2 powders, even for relatively high solid content suspensions of up to 15 vol%. Fifty‐micrometer‐bead milling was also able to disperse aggregates to the same sizes as the ultrasonic irradiation method, but 50‐μm‐bead milling can be used only in relatively low solid content suspensions. It was concluded that the ultrasonic dispersion method was a useful way to prepare concentrated and highly dispersed nanoparticle suspensions.