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1 2005

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Nanosilica Partially Modifiedby Hexamethyldisilazane in Air

Gun'ko V., Voronina O., Voronin E., Zarko V., Pakhlov E., Leboda, Skubiszewska-Zięba J., Janusz W., Chibowski S.

Polish Journal of Chemistry

2005

Vol. 79 / nr 11

1787-1804

Unmodified and modified nanosilicas containing different content of trimethylsilyl (TMS) groups grafted by interaction with various amounts of hexamethyldisilazane (HMDS) in a reactor contacting with air were studied using infrared spectroscopy, adsorption and potentiometric titration methods. Contribution of narrow gaps between spherical primary silica particles forming aggre gates decreases with in creasing TMS loading (tetaTMS), because of blocking of these gaps by grafted functionalities. Contribution of broader gaps corresponding to mesopores de ends slightly on tetaTMS, and changes in contribution of macropores are rather random. IR spectra of modified samples depict changes in bands of the O-H stretch ingvibrations at 3750 and 3300 cm-1 (reduced with qTMS) and 3680 and 3500 cm-1 (changed nonlinearly with qTMS), since HMDS can interact with silanols and ad sorbed water and af fect the ad sorbed amounts of water. Enhance ment of the hydrophobic properties of the surface reduces the amounts of adsorbed water, and the IR band in tensity at 3300 cm-1 di minishes. The adsorption of poly(vinyl pyrrolidone) on silicas decreases with tetaTMS in consequence of changes in the surface structure and the reduction of adsorption potential. The silylation diminishes the su face charge density and the electrostatic surface poten tial, and the point of zero charge shifts to ward larger pH values with in creasing tetaTMS value.