The change in wettability and structure of silica powder surfaces modifiedwith hexamethyldisilazane

The wettability and surface structure of precipitated silica surface loaded trimethylsilyl groups were investigated. By measuring water and nitrogen a dsorptions, it was found that the nontreated sample had micropores. The por es with a diameter less than 0.8 nm were not modified, while the pores with a diameter from 0.8 to 0.9 nm were modified by trimethylsilyl groups and c losed by them. From these results, it was assumed that the former pores wou ld become sites for water vapor as surface silanol groups after modificatio n and the latter pores would be independent of water adsorption. The charac ter of the silica bare surface disappeared above a surface conversion rate of 33%. These results are deduced from neopentane adsorption experiments. F urthermore, the water adsorption capacity near saturated pressure, as an in dex of micro-wettability, did not reach the theoretical monolayer capacity above the same conversion rate (33%). It was also indicated that the prefer ential dispersion property as an index of macro-wettability drastically cha nged at a conversion rate of about 33%. From these results, it was demonstr ated that the wettability is closely related to the surface structure inter fering with the adsorption of water.