ADSORPTION LAYERS OF WATER ON THE SURFACE OF HYDROPHILIC, HYDROPHOBICAND MIXED SILICAS

The H-1 NMR technique was used to study the hydration activity of hydr ophilic (Aerosil A-300), methylated (MS) and mixed in a 5:1 ratio (MIX ) silicas. It has been determined that the thickness of a layer of ads orbed water in an aqueous medium becomes higher for MS compared with t hat for A-300. The above phenomenon may be explained by polarization o f the adsorbent particles. Hydrophobic and hydrophilic particles in th e MIX sample are bound together by the strong electrostatic interactio ns. H-1 NMR spectra of adsorbed water are characterized by the appeara nce of a new signal having an anomalously low value of chemical shift (delta = 1 ppm), which may be caused by water molecules forming the su rface-hydrated complex carrying a negative charge. The appropriate val ues of the free surface energy of adsorbents have been calculated. (C) 1998 Elsevier Science B.V.