Silica maximally hydrated

F or silicas with no surface siloxane groups (sO Call maximally hydrated silicasf), the total concentration of surface hydrcpcyJs is approximately constant at 4 to 5 hydroxyls per 100 of surface.. iTFese values are... 

There is a correlation between the amount of adsorbed methane and WAW (Figure 1.44d). Lower amounts of adsorbed methane is observed for samples at minimal (/ =0.005 g/g) and maximal (1 g/g) hydration of silica. The former includes too little water to form effective nanoporosity (between the surface of adjacent silica nanoparticles, clusters, and domains of unfrozen water and ice nanocrystallites), and the latter includes too much water, which can form a nearly continuous surface SAW film (Figure 1.44a), and bound water is less clustered. In other words, strong clustering of bound water (Figure 1.46 Table 1.13) is a necessary condition for the maximal adsorption of methane onto nanosilica. 

Thus, the adsorption of methane onto nanosilica A-300, composed of nonporous primary nanoparticles (average diameter 8.1 nm), at standard pressure is a function of temperature and silica hydration. The silica hydration dependence is nonlinear, and maximal adsorption of methane (1.9-1.2 wt% at 200-280 K) is observed at hydration h = 0.l g/g for intact silica. Decrease (on heating) and increase (on wetting) of the silica hydration both lead to a reduction of methane adsorption. Coadsorption of methane and water leads to the appearance of a H NMR signal from WAW at 8h 1 ppm. The amount of this water correlates to concentration of adsorbed methane, because weakly associated bound water is most clustered at the surface of nanosilica composed of nonporous primary nanoparticles. The adsorption of methane on nano/mesoporous... 

Thus, water bound to nanosilica does not form uniform layers even at relatively high hydration (1 g of water per 1 g of dry silica). Coadsorption of water with weakly polar chloroform alone or in a mixture with polar DMSO or acetonitrile more strongly affects the structure of water bound to nanosilica A-380 at lower hydration when significant portion of silica surface remains uncovered by water. Maximal clusterization of bound water is observed on the coadsorption with chloroform/ DMSO mixture because DMSO can effectively interact with both nonpolar (through dispersion interactions of chloroform with CH3 groups) and polar (water interaction with the S=0 bonds) structures. 

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