Mesoporous silica nanoparticles (MSNs) with uniform size (<50 nm) yet with different pore diameters were synthesized, and used as fillers in poly(ether sulfone) (PES) films in order to decrease their coefficient of thermal expansion (CTE) without sacrificing optical transparency. Here, both CTE and optical transparency of the MSN/PES nanocomposite films gradually decreased with increasing MSN concentration. The PES films containing MSNs with larger pores showed the best performance in CTE and optical transparency. While the CTE decreased by 32.3% with increasing MSN content up to 0.5 wt%, the optical transparency decreased by only less than 6.9% because of the small and uniform particle size of less than 50 nm, which minimizes light scattering. This pore size effect is more clearly observed via an annealing process, which enables the polymer chains to slowly move and fill in the free volume in the pores of the MSN, and thus restricts the thermal motion. The effect of the silica nanoparticles was investigated not only on the thermal stability but also on the mechanical stability. We expect the MSNs synthesized in this study to be used as a promising filler to enhance the thermal and mechanical stability of the PES substrate without sacrificing its optical transparency.
Ammonium hexafluorosilicate (AFS) in aqueous solution under mild conditions can modify drastically the textural properties of Ca-A zeolite. Open slit-shaped mesopores with a pore-size distribution showing a maximum at 14-20nm are formed. The average pore diameter depends on the rate of addition of the AFS solution to the leaching medium. If such a treatment is combined with acid leaching or hydrothermal treatment, the mesoporous materials obtained exhibit similar pore-size distribution. However, their adsorption capacity for nitrogen is significantly increased.
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