A novel interpretation of pH-dependent microstructure and rheology evolution in silica suspension based on interparticle interactions

We suggest a new interpretation for pH-dependent temporal evolution in the microstructure and rheology of silica suspensions based on interparticle interactions, which differs from the conventional explanation including the catalytic effect of hydroxyl ions and charges. The temporal evolution of silica suspensions under various pH conditions was investigated through rheometry and diffusing wave spectroscopy (DWS) analysis. The transition from liquid to solid was observed to be the most rapid at pH 5 compared to other pH conditions (pH 3, 7, 9). This phenomenon could not be adequately explained by the conventional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory that predicts the liquid-to-solid transition occurs more rapidly at the lower pH condition due to the lower surface charge. As an alternative, we employed an elaborated DLVO theory that additionally considers the hydration force, arising from the hydrophilic nature of the silica surface. The pH dependency was interpreted using the elaborated DLVO theory, which showed that the strong short-range nature of the hydration force significantly reduced the attraction range at pH 3, leading to the retardation and decline in structural and rheological development. The impact of pH and resulting alterations in interparticle interaction on the microstructure were further investigated using rheological scaling theory. Graphical Abstract