Mechanical properties of thin films at the dodecane-water interface, for multilayered emulsion applications

Abstract The use of polyelectrolyte multilayers (PEMs) as emulsifying layers at an oil-water interface has significant potential to enhance emulsion application and function. In spite of this potential, there are few studies that directly probe the mechanical properties of interfacial layers of PEMs at the oil-water interface, properties that will influence significantly their range of applicability in emulsion science. We report here a study where we have explored the formation and mechanical properties of polystyrene sulfonate (PSS) and polydiallyldimethylammonium chloride (PDADMAC) multilayers at an oil-water interface. The study of mechanical properties as a function of layer number has revealed differences for the interface depending on the identity of the multilayer terminating layer. Specifically, PDADMAC-terminated films were much more resistant to deformation and remained elastic over a much larger percentage deformation than the films terminated with PSS. The effect is seen to persist with each bilayer, with the interface cycling between elastic/deformable up to the measured maximum number of bilayers. Within this outer layer effect data, the range of the determined mechanical properties were: surface shear moduli ranging between 35 and 60 mN ∙ m − 1 ; bulk shear moduli ranging from 0 to 10 MPa. The data indicate that there is promise in the use of PEM emulsifying layers, allowing for tailoring of the physical stability of emulsion droplets, and thus aiding in prolonging product stability and shelf life.