Inversion of Hofmeister Series by Changing the Surface of Colloidal Particles from Hydrophobic to Hydrophilic

Abstract

In this paper, we demonstrate that in addition to the nature of the ions the nature of the surface is also of vital importance in order to elucidate the origin of Hofmeister effects. Specifically, we show that for the solid/water interface when the surface turns from hydrophobic to hydrophilic, an inversion in the Hofmeister series occurs. Results were recorded from colloidal-stability experiments performed with seven different anions located at different positions in the Hofmeister series and working with four colloidal systems that varied in their surface-charge sign and hydrophobic/philic degree. A mechanism based on the structural modifications that ions and surfaces induced in water is proposed to explain all these results. The existence of hydration forces on hydrophilic systems enables us to explain the data and to reinforce our arguments concerning the relevance of considering the water structure around both the ions and the interfaces on Hofmeister effects.