Low-energy bead-milling dispersions of rod-type titania nanoparticles and their optical properties

The low-energy dispersion of nanomaterials in the bead-milling process is examined. The effect of milling parameters including bead size, rotation speed, and milling time on the dispersibility of fragile rod-type titanium dioxide nanoparticles is investigated. From experimental data obtained for the morphological, optical, and crystalline properties of dispersed nanoparticles, an unbroken primary particle dispersion in colloidal suspension was obtained only by conducting the bead-milling process using the optimum milling parameters. Deviation from the optimum conditions (i.e., higher rotation speed and larger bead size) causes re-agglomeration phenomena, produces smaller and ellipsoidal particles, and worsens crystallinity and physicochemical properties, especially the refractive index, of the dispersed nanoparticles. We also found that decreases in refractive index induced by the milling process are related to collisions forming broken particles and the amorphous phase on the surface of the particles. In addition, the present low-energy dispersion method is prospective for industrial applications, confirming almost no impurity (from breakage of the beads) was apparent in the final product.