Résumé
Colloid and interface science has been developed in many aspects and now many phenomena taking place in the colloidal scale and/or at the interface are well described by theory and fully addressed by experiments. However, some fundamental and "old" problems have remained unsolved up to now. Here, I would like to address the "simple" case of contact angles (CAs) of submicron particles at the water interface. Is the macroscopic CA, measured by the wetting angle of a water drop on a macroscopic substrate, the same as the CA of a submicron particle at the water interface? In this presentation, I will explain how to measure in-situ CAs of colloidal particles at the fluid interface using ellipsometry, compare different CAs measurements and discuss the role of electrostatics at the water surface.