Coupling static multiple light scattering (SMLS) analysis with the Hansen approach for the rationalization of the dispersibility and colloidal stability of TiO2 particle dispersions

Abstract

While the characterization of dispersibility and colloidal stability remains a key step in many formulation processes, these notions are still confused, and colloidal stability is often interpreted as a direct consequence of dispersibility. In this study, Static Multiple Light Scattering (SMLS) measurements and the predictive Hansen approach are combined to distinguish and characterize the dispersibility and the colloidal stability of TiO2 P25 particles dispersed in pure and mixture of solvents. To this aim, an experimental protocol is proposed using fast time resolved SMLS measurements at a fixed height to assess suspension dispersibility under mechanical stirring as well as space and time resolved SMLS measurements of the suspension stability at rest. Dispersibility is quantified through a Dispersibility Index (DI) depending on the mean diameter of particles and transmission or backscattering signals standard deviation measured with SMLS under mechanical stirring. Quantification of colloidal stability is obtained from a Relative Turbiscan Stability Index (RTSI) measured at rest. Scoring of solvents is performed using the DI and the RTSI to build Hansen dispersibility and stability spheres respectively. It is found that the dispersibility and the stability spheres are clearly separated arguing that a lower colloidal stability is not necessarily a consequence of a poor dispersibility. Beyond this clarification, this combined SMLS-Hansen approach is a major step toward the optimization of dispersibility and stability of formulations. It can be also intended to find better dispersion media, greener and cheaper solvents to optimize particles suspensions, to reduce the content of costly stabilizing additive or to satisfy product regulatory requirements evolution.