Composition and pH dependence on aggregation of SiO₂–PVA suspension for the synthesis of porous SiO₂–PVA nanocomposite

Porous monolithic SiO₂–poly(vinyl alcohol) (PVA) nanocomposites were fabricated by drying an SiO₂–PVA suspension. Depending on the amount of added PVA and pH value of the suspension, the Brunauer–Emmett–Teller surface areas, total pore volumes, and mean pore radii of the (100 − x)SiO₂–xPVA (x = 0, 10, 20, 30 wt%) nanocomposites were 102–313 m² g⁻¹, 0.61–1.42 cm³ g⁻¹, and 8.1–14.7 nm, respectively. Some cracks were observed in the monolithic SiO₂–PVA nanocomposite, affected by the pore size. To elucidate crack generation, the correlation between the dispersion/aggregation in the SiO₂–PVA suspension and the pore size distribution of the nanocomposite was evaluated in terms of the added PVA amount and pH value. At x = 20 and pH 3, the SiO₂ particles and PVA aggregated in the suspension. The preparation of crack-free monolithic SiO₂–PVA nanocomposites was possible using the aggregated suspension owing to the low capillary force during drying because of the relatively large pores.