Interfacial Shear Rheology without an Interfacial Geometry

We have developed an experimental method to perform interfacial rheology on liquid/liquid interfaces with no tool attached directly to the interface. This is achieved by shearing one of the liquid phases and measuring the interfacial response via confocal microscopy. Using this method we have measured steady shear material parameters such as the interfacial viscosity for fluid-like interfaces, and the interfacial elastic modulus for interfaces with solid-like behaviour. These measurements are in line with recent measurements made on similar systems using a conventional probe. Moreover, using our method we are able to measure lower interfacial viscosities than those that have previously been reported. This indirect method lends itself to microscopic structural analysis, as well as macroscopic rheological analysis, due to simultaneous microscopy. Our analysis shows that the interfacial behaviour is strongly dependent on the surface coverage and surface structure, and steady shear can have an irreversible effect on the structure of an interface.