Size-dependent aggregation behavior in monodisperse silica: a nitrogen adsorption study

The present study focused on the aggregation behavior that resulted from surface interaction between monodisperse silicas synthesized with Stober method using nitrogen adsorption method at cryogenic temperature (77 K). Specific surface area, pore size distribution and surface fractal dimension from adsorption isotherm were evaluated. For relatively large particle, (190 nm in diameter), it was observed that nitrogen adsorption isotherm could be classified to type I. However, others with small size (below 100 nm) have shown the characteristic of type IV with the evident character of hysteresis loop in the isotherm. The increment of specific surface area (S-BET) changed with the decrease of particle size, which could be fitted with an exponential decay equation. Pore size distribution (PSD) indicated that there exist an amount of mesopore (between 2 and similar to 50 nm) and shift toward the smaller with decreasing the size of silica. Surface fractal dimension (D-SF) from thermodynamic method demonstrated that the D-SF increased with the decreasing the size of silica. PSD and D-SF clearly embodied the size-dependent aggregation of monodisperse silica nanoparticle, which could be used to explain the inferior performance of polymer nanocomposite filled with smaller monodisperse silica. Copyright (C) 2011 John Wiley & Sons, Ltd.