Investigation of Electrical Double Layers on SIO2 Surfaces by Means of Forcevs. Distance Measurements

The formation of electrical charges at solid/liquid interfaces results in a diffuse electrical double layer close to the solid surface. This layer determines, for example, the behaviour of ceramic particles in aqueous media and the effective pore radius of membranes acting in liquids. The SiO2/SiO2 system is used to demonstrate that linear measurements using atomic force microscopy are suited for characterizing double layers at real surfaces. It has to be taken into consideration that the tip itself, which is acting as the probe, is also surrounded by a double layer and responds to the composition of the electrolyte in a material-specific way. For this reason an oxidized silicon tip was used for the present investigations, so that tip and sample consisted the same material. In this way it is possible to obtain results that can be evaluated easily and compared with the DLVO theory.