Chemistry Reference
In-Depth Information
The nature of the silica-water interface is determined by adsorption/desorption
of the species in the water. When a silicon oxide, e.g., quartz, is fractured, the initial
surface is composed of dangling silicon and oxygen bonds (Fig. 4.30a) which are not
stable and hydroxylate easily with available water.
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The hydroxylated surface is
dominated by SiOH groups (Fig. 4.30b). The initial adsorbed water adjacent to the
surface is oriented and has properties different from the bulk water. As this adsorbed
water layer increases to more than three monolayers, its properties become more like
bulk water. The surface potential changes as a result of the adsorption of the ionic
species in the water.
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The interaction of the hydroxyl groups with the protons in the water establishes
an interfacial layer with a pH-dependent surface charge and potential. According to
