Ion-specific effect on the gelation kinetics of concentrated colloidal silica suspensions.

The comparative gelation kinetics of concentrated colloidal silica suspensions at pH 9.8 has been studied in the presence of two different counterions, ammonium as a representative structure-breaker ion and sodium as a representative structure-maker ion. For the same ionic strength of 0.45 M, the experimental results have indicated a pronounced effect of the ion-specificity on the aggregation kinetics and on the microstructure of the gelified networks at the sol-gel transition. This was ascribed to the significant difference of the critical coagulation concentration value in the presence of the two electrolytes.