Unmodified pyrogenic silica PS300 and partially silylated nanosilica samples at a degree of substitution of surface silanols by trimethylsilyl (TMS) groups Theta(TMS) = 27.2% and 37.2% were studied to elucidate features of the interfacial behavior of water adsorbed alone, or co-adsorbed with methane, hydrogen, or trifluoroacetic acid (TFAA). In the aqueous suspension modified PS300 at Theta(TMS) = 37.2% forms aggregates of 50200 nm in size and can bind significant amounts of water (up to similar to 5 g/g). Only 0.5 g/g of this water is strongly bound, while the major fraction of water is weakly bound. The presence of surface TMS groups causes the appearance of weakly associated water (WAW) at the interfaces. The adsorption of methane and hydrogen onto TMS-nanosilica with pre-adsorbed water (hydration degree h = 0.05 or 0.005 g/g) increases with increasing temperature. In weakly polar CDCl3 medium, interfacial water exists in strongly (SAW, chemical shift delta(H) = 4-5 ppm) and weakly (delta(H) = 1-2 ppm) associated states, as well as strongly (changes in the Gibbs free energy -Delta G > 0.5-0.8 kJ/mol) and weakly (-Delta G < 0.5-0.8 kJ/mol) bound states. WAW does not dissolve TFAA but some fraction of SAW bound to TMS-nanosilica surface can dissolve TFAA. (C) 2014 Elsevier Inc. All rights reserved.