Effect of the Synthesis Methods on Hydrophobic Properties of Modified Silicas

摘要

Composites based on fumed silica with surface hydrophobic groups were synthesized by chemical substitution of silanol groups' proton for trimethylsilyl (TMS) groups, adsorption of poly(dimethylsiloxane) (PDMS) and combined chemical-adsorption methods. Microcalorimetry measurements and values of the wetting contact angle with water (Theta) were obtained to investigate the hydrophobic properties of prepared materials. The hydrophilicity indexes (K-h) were determined from the relationship of heat of immersion in water Q(w) to non-polar decane Q(d). The Theta and Q(w) demonstrated changes with increase of modification degree (d(m)) for composites containing a monolayer of PDMS. All samples with excess of PDMS had high Theta (> 110 degrees) and relatively low Q(w) and K-h. Composites modified with TMS groups demonstrated hydrophobic properties in accordance with K-h at d(m) 0.7, whereas Theta > 90 degrees is observed only for those samples with d(m) = 1.0. The different methods of synthesis may be applied based on the morphological characteristics and hydrophobicity of the samples.