STUDIES OF WATER ADSORBED IN POROUS VYCOR GLASS

Properties of water adsorbed in porous Vycor glass and Vycor glass tre ated with hexamethyldisilazane (HMDS) have been studied by measuring N MR as a function of water content and temperature and observing penetr ation of water into the pores. Some of the observed properties are com pared with those of methanol and ethanol. The NMR linewidth of water i n original glass pores is proportional to the fraction of water in a s urface monolayer on the glass. The melting point depression of the por e water is inversely proportional to the pore radius, and ice water in terfacial tension is evaluated as 27.5 mN/m. When treated glass was im mersed in water, liquid water could not penetrate the glass sample, wh ich had more than 0.4/nm(2) trimethylsilyl group substituted for surfa ce hydroxyls; however, the alcohols could still easily penetrate the f ully treated glass, which had 1.3/nm(2) trimethylsilyl groups. Water a dsorbed in weakly treated glass shows broadening of the NMR line; cont rastingly, the alcoholic hydroxyls show narrowing of the lines. The fr eezing and melting point of pore water rise with surface treatments. T hese phenomena can be explained in terms of structure forming of adsor bed liquid on the surfaces and the interaction between the molecules i n the structured layer and the subsequent layer. (C) 1996 Academic Pre ss, Inc.