The effects of surface silanol and nano-scale structure on the surface interaction force between solid surfaces in water were studied using silica gels prepared from alkoxide via acid-catalyzed hydrolysis under various conditions. The factors considered in the present study were catalyst type and H
2O/TEOS mole ratios. The surface silanol structure, the interaction between solid surfaces and the inner structure of dried-gels were determined, respectively, by a FT-NIR, FT-IR, Atomic Force Microscope (AFM) and a mercury porosimeter. As a result, when H
2O/TEOS mole ratio (from 4 to 40) was relatively low during acid-catalyzed hydrolysis, almost all of the surface silanols were hydrogen-bonded without free silanols. Since the hydrogen-bonded silanols formed a hydrogen-bonded water layer on silica surface, additional short-range hydration force (shorter than 2nm) appeared between the solid surface and the tip of AFM. Gel structure and force between surfaces markedly varied depending on the type of catalysts. When HCl was used as an acid catalyst, the surface structure of silica gel was very smooth and the force curve between the AFM tip and gel surface was described approximately by DLVO theory for the silica gels prepared at any H
2O/TEOS mole ratios. On the contrary, in the case of nitric acid catalyst, the roughness and pore diameter of silica gels were larger than those of silica gel prepared with HCl, and the force curve between gel surfaces and the AFM tip could not be explained by DLVO theory.
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