Dispersion of submicron-sized SiO 2 /Al 2 O 3 -coated TiO 2 particles and efficient encapsulation via the emulsion copolymerization of methacrylates using a thermoresponsive polymerizable nonionic surfactant

Submicron-sized SiO 2 /Al 2 O 3 (Si/Al)-coated titanium dioxide (Si/Al-TiO 2 ) particles were encapsulated through the emulsion copolymerization of methacrylates using a thermoresponsive polymerizable nonionic surfactant, NE-10. An optimized water-dispersion method was developed to disperse Si/Al-TiO 2 dried powders after various methods were investigated, such as using an ultrasonic homogenizer, a paint shaker, and a pot mill rotator (PMR) in the presence of partially neutralized poly(isobutylene- alt -maleic acid). The ultrasonic homogenizer successfully dispersed Si/Al-TiO 2 in water, whereas the paint shaker and PMR caused overdispersion and broke the SiO 2 /Al 2 O 3 shell. The optimal dispersion of Si/Al-TiO 2 was obtained under the following conditions: 40 wt% solid content, 0.3 mm SiO 2 beads, 0.25 wt% ISOBAM-600 (neutralization degree = 0.7), rotating speed <100 rpm, and rotating time <4 h. The encapsulation efficiency ( F en ) was affected by the monomer and initiator types, NE-10 and sodium dodecyl sulfonate concentrations, and whether the process was batch or semibatch. The NE-10 concentration exhibited a significant effect on F en ; the optimal NE-10 addition was 1.4–2.5 mg for 1.0 g of Si/Al-TiO 2 . F en > 90% was achieved using 0.25 g methyl methacrylate and 0.75 g n -butyl methacrylate, following a two-step semibatch emulsion copolymerization under optimized conditions. Compared to bare Si/Al-TiO 2 , the encapsulated hybrid particles showed a higher reflectance and dispersion stability in water.