Hansen sphere obtained for TiO2 particles
Formulating stable particle suspensions is of great interest for academics and industrials as it allows them to enhance the properties and the lifetime of their products. Overall, the choice of the stabilization medium is the key factor to avoid particle agglomeration before adding additives (surfactants, polymers, etc.) which are, most of the time, quite expensive. Hansen’s approach can be adapted to describe the particle stability in various solvents by using three different parameters, δD, δP, and δH, which are representative of the interactions between the particle and the dispersion media.
In that view, each particle or solvent can be represented by a point in a 3D-space with these parameters as coordinate values. The particle stability is evaluated considering a range of known solvents exhibiting a large variation in these 3D spaces, followed by a ranking of the tested solvents as good or poor stabilization media. The border between good and poor solvents allows the building of a sphere with a center corresponding to the Hansen parameters of the particle. If another solvent is situated inside the sphere, it can be considered as a good stabilization media. Inversely, a solvent situated outside the sphere should poorly stabilize the suspension. In that way, the TURBISCAN Stability Index (TSI) is well adapted to score each solvent toward its ability to stabilize TiO2 particles, and so, to build the corresponding Hansen sphere.
Hansen sphere obtained for TiO2 particles
By using the TURBISCAN technology, it is easy to discriminate in an accurate way the tiny stability variation of solvents tested as good dispersion media, which is quite difficult by conventional observation. These precise measurements allow generating a Hansen sphere, which is more relevant and restrictive than the ones obtained through the visual characterization of samples as it is classically realized.
Besides the prediction of other solvents as good or poor stabilization media, a classification of the solvent stabilization properties can be also predicted considering that the lower the distance between the solvent and the sphere center, the more stabilized suspension should be obtained.
In that way, increasing the suspension stability using a mixture of different solvents can be also deducted from the sphere representation, such as the Ethanol / DMSO mixture. Indeed, due to the specific positions of Ethanol and DMSO located at opposite borders of the TiO2 Hansen sphere, it is quite easy to formulate a mixture of these two solvents, which is much closer to the sphere centre and which provides a better suspension stability.
Stability performance improvement of TiO2 suspension with Ethanol / DMSO mixture compared to other solvents
This approach can also be employed to predict greener and cheaper solvents to optimize particle formulation regarding the content of costly stabilizing additives or product regulatory requirements evolution. Another field of application could be the stabilization of battery slurries during storage, for which the use of these additives is not relevant compared to the stabilizing properties optimization of the dispersion media.
