Wetting of Emulsions Droplets: From Macroscopic to Colloidal Scale

By using large oil-in-water droplets covered with ionic surfactant we measure contact angles to deduce the adhesive energy between macroscopic interfaces as a function of the temperature T and the salt concentration C. A wetting transition takes place at a well defined temperature T*(C). At the colloidal scale, we have observed that submicron droplets covered by the same monolayers undergo a phases separation. We show that the phases diagram can be quantitatively predicted from the macroscopic contact angles. However, to describe the colloidal phase separation we have to account for both the entropy and the deformation induced by the wetting of the droplets. Finally, our results show how the macroscopic wetting transition can be shifted at the colloidal scale where droplets entropy plays an important role.