Cation effects, in silica gel formation

The influence of the cations and anions has been discussed separately with the solution properties and reactions in the main focus. It has, however, been known over 100 years that anions play a crucial role for the stabilization and coagulation of colloids. More recently, the contribution of anions on the stabilization of particles, biocolloids, and bubbles has received renewed attention. - In these papers, it has been pointed out that there exists a collaborative interaction between cations and anions upon adsorption of one of the complexes from solution. At high concentrations this effect renders the simple indifferent ions specific and selective to each other. It is also seen as a dependency on the acid-base pair chosen for the regulation of the pH. This effect certainly needs to be added as an extension to (correction of) the DLVO theory. However, as shown in this paper, it is just as probable that the anion and cation collaborate during the adsorption and formation of gels and precipitates at the surface. The presence of such mixed phases has been confirmed experimentally, e.g., during the formation of hydroxoapatite in silica gel layers. ... 

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