Zeta potentials of monodispersed, spherical silica particles in mixed solvents as a function of cesium chloride concentration

Zeta potentials of silica are negative in most mixed solvents (99% organic co-solvent, 1% water), but in t-butanol and pyridine they are positive. When CsCl is added to the suspension as a probe substance, two types of behavior are observed. In solvents of ε>25, the ζ potential asymptotically approaches zero, while in solvents of lower dielectric constant, the sign of ζ potential is reversed to positive at a sufficiently high CsCl concentration, crev. In order to evaluate the nature of interaction leading to different solvent responses, a range of frequently used solvent scales relating to specific interactions between the components of the system were compared. A moderate correlation was found between crev for silica and one solvent property alone, and those previously found for anatase, respectively. Using linear combinations of two solvent scales improved the correlation, but it was still not satisfactory. However, considering separately the contributions from both solvent components, a nearly statistically significant correlation was found. The results are evaluated considering the particular behaviour of each solvent group, and the specific influence of the material properties of silica and of possible impurities present in the system.