(a)
before the cleaning of porous silica, (b) the surface-adhered
nanoparticles on porous silica and (c) before the cleaning of
nonporous fused silica. A multilayer packing of nanoparticles
was formed on both the types of silica particles. The thickness
and number of nanoparticle layers for nonporous silica were
greater than those for porous silica particles. Each silica particle
was cleaned in a water bath equipped with an ultrasonic
disperser (SND Co., Ltd, US-3, 38 kHz) using ultrapure water.
To measure the bulk powder behavior, mica (YamaguchiMica
Co., Ltd., Mica Powder Y-2300) was used as the test sample.