The behavior of water at the modified silica interface.
The behavior of water at the modified silica interface was studied with Differential Scanning Calorimetry. A model for the interaction of water with the surface of silica was evolved to include the influence of the silica surface, the modification of the surface with hydrophobic and hydrophilic functional groups, and the presence of organic solvents. Initial studies involved the investigation of the melting behavior of water at the surface of unmodified silica. This was studied as a function of pore size, specific surface area, surface activity and specific pore volume. The perturbation of the water in the near surface region by interactions with the surface silanols and the curvature of the silica surface resulted in the observation of a melting peak was that was significantly different than the bulk water behavior. Changes to this peak were observed as a function of the modification of the silica surface with alkyl chains of varying chain length, and variations in the bonding density of these chains. As a consequence of the modification of the surface, the water was able to interact with only isolated silanol sites and this was reflected in a shift in the melting peaks. The deactivation of the silanol sites occurred both through the formation of the silyl ether linkage to the modifier, and the blocking of the surface by the hydrophobic alkyl chains. The changes in the behavior of water at the modified silica interface in the presence of organic solvents were also investigated. It was found that the ability of the organic solvent to hydrogen bond to the silica surface and with water was the greatest contributor to the changes in the melting behavior of the water. The behavior of water at the silica interface modified with hydrophilic functional groups was investigated. It was found that the functional groups that could hydrogen bond with the water could also influence its melting behavior. As a consequence the layer of water affected by the surface was extended further away from the surface than was observed with unmodified silica.
Dissertations, Academic., Chemistry, Analytic.
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