Structure and Yielding of Colloidal Silica Gels Varying the Range of Interparticle Interactions.

The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by s…