Features of fumed silica coverage with silanes having three or two groups reacting with the surface

Fumed silicas modified by 3-methacryloyloxypropyltrimethoxysilane (MAPTMS), methacryloyloxymethylenemethyl diethoxysilane (MMDES), and 3-aminopropyltriethoxysilane (APTES) were studied by means of TPD-DTG, IR, 1H NMR, electrophoresis, photon correlation spectroscopy, and theoretical methods. The modification of fumed silica by these silanes strongly changes the ζ(pH) potential and the particle size distribution in aqueous suspensions depending on the amounts and the structure of a modifier. MMDES gives the better results in comparison with its mixture with APTES or individual MAPTMS in order to reduce the particle (agglomerate) size of modified silica at the modifier concentrations over the 0.05–0.2 mmol/g range. Grafted silanes reduce the hydrophilic properties of silica depending on the pretreatment conditions. Bound MMDES diminishes the ζ potential in contrast to MAPTMS, which markedly magnifies negative ζ potential at pH>5 due to large amounts of residual SiOR groups hydrolysed in the suspensions.