Microscopic Origin of the Hofmeister Effect in Gelation Kinetics of Colloidal Silica

Abstract

The gelation kinetics of silica nanoparticles is a central process in physical chemistry, yet not fully understood. Gelation times are measured to increase by over four orders of magnitude, simply changing the monovalent salt species from CsCl to LiCl. This striking effect has no microscopic explanation within current paradigms. The trend is consistent with the Hofmeister series, pointing to short-ranged solvation effects not included in the standard colloidal (DLVO) interaction potential. By implementing a simple form for short-range repulsion within a model that relates the gelation time-scale to the colloidal interaction forces, we are able to explain the many orders of magnitude difference in the gelation times at fixed salt concentration. The model allows to estimate the magnitude of the non-DLVO hydration forces, which dominate the interparticle interactions at the length-scale of the hydrated ion diameter. This opens the possibility of finely tuning the gelation time-scale of nanoparticles by just adjusting the background electrolyte species.

Influence of Co-Ion Nature on the Gelation Kinetics of Colloidal Silica Suspensions

“…However, at the same ionic strength gelation was faster when the cationic counterion of chloride salts was more chaotrope. 6 The first proposed argument has been ascribed to charge screening effects. For pH conditions much greater than the iep of silica, the interfacial hydrogen-bonding network of water molecules at the negatively charged silica surface is not well developed.…”

Specific Anion Effects on the Kinetics of Iodination of Acetone

“…The aim of this work is to investigate the Hofmeister (specific ion) effect on the kinetics of iodination of acetone in acidic conditions. To the best of our knowledge, this is the first contribution that addresses the effect of the acid nature on the kinetics of iodination of ketones, and one of the few studies on Hofmeister effect in chemical kinetics in solution …”

“…To the best of our knowledge,t his is the first contributiont hat addresses the effect of the acid nature on the kinetics of iodinationo fk etones, and one of the few studies on Hofmeister effect in chemical kinetics in solution. [15][16][17][18]…”

Influence of the Counterion Nature on the Stability Sequence of Hydrophobic Latex Particles

“…Within these conditions, where fewer neutral SiOH silanol groups are present at the silica surface, the adjacent aqueous layers are not well structured so that an enhanced accumulation of alkali cations with increasing chaotrope character was observed. 28 3.3. Comparative Effect of Co-Ions with Counterions of Different Lyotropic Nature.…”