Fig. 8 shows the AS measurement results for each particle
mixture. For porous silica (P-1500), the AS value increases by
15.40% from 8.90 to 10.27 after the removal of surface-adhered
nanoparticles by ultrasonic cleaning. For nonporous silica (FB-
6S), the AS value increases by 47.21% from 8.24 to 12.13 after
cleaning. These results suggest that surface-adhered nanoparticles
on silica powder decreased the aggregation behavior.