Dynamic Surface Tension Study of Solid Nanoparticles Adsorption at a Water/Oil Interface

The objective of this study focused is understanding the mechanisms involved in the stabilization of water/oil interfaces by solid nanoparticles (NPs). Magnesium oxide and magnesium hydroxide of different sizes and in different electrolytes concentrations were studied and compared, at a model water/cyclohexane interface, in a drop tensiometer. Gradual interfacial adsorption of NPs, initially dispersed in water, were followed by tensiometry. Indeed, the model interface was maintained and observed in a drop tensiometer, analyzed through the axisymetrical drop shape analysis (ADSA), in order to determine the interfacial properties. Owing to the direct relationship between Pickering emulsion (emulsions stabilized by solid nanoparticles) stability and the interfacial properties of these layers, different nanoparticulate systems were compared, magnesium hydroxide (Mg(OH)₂) NPs, magnesium oxide (MgO) NPs, with different size. In addition, the concentration of electrolytes (NaCl) in the bulk phase was shown to induce a partial NPs aggregation (so-called NPs flocs), with an important incidence on the interfacial layer stability. Dynamic interfacial tension data will be analyzed using the classical Ward and Tordai model. Dynamic surface tension measurements revealed a sharp decrease of interfacial tension with MgO NPs and Mg(OH)₂ NPs without NaCl. For the flocs of nanoparticles aggregated that forms obtained with the presence of NaCl 2mM, a slow decrease of interfacial tension was observed unlike individual nanoparticles.