Abstract
The authors have investigated a pre-control of loosely agglomerated structure of silica nanoparticles as filler component used for the fabrication of organic/inorganic nanocomposites by a blending method. The packing structure and void fraction of the agglomerate of silica nanoparticles that affect a dispersibility of their particles in polymer matrix were controlled by destabilizing a nano-sized silica sol via pH control and salt addition. It was found that three dimensional networks of nano-silica are formed in the pH-controlled sol due to a silica-silica bridging through coordination with flocculating cations of added salt. As another role of the added salt, its crystal seemed to act as a template that enlarges void spaces inside the silica network as the solvent evaporation progresses. The silica agglomerate with the highest void fraction (～0.49) could be prepared by controlling pH of sol （≧4） and the ratio of volume of added salt to that of colloidal silica (≧1/9) under the present experimental conditions.
