A novel and noninvasive approach to study the shear rheology of complex fluid interfaces

Surfactants at gas-liquid and liquid-liquid interfaces have profound effects on interfacial stresses that strongly influence flow in bulk phases in contact with the interface. These effects include changes in interfacial tension and the development of extra stresses that arise when the interface is deformed. Surfactants are important in nature, biological function, and numerous technologies. Understanding interfacial rheology is critical to the development of improved surfactants for these important applications. Here, we propose a novel and noninvasive technique for the investigation of interfacial rheological behavior in shear deformations. In recent years, several techniques for such measurements have been developed and utilized to study a wide range of surfactant systems. However, existing techniques may inherently be invasive making it difficult to isolate the intrinsic interfacial rheological behavior from disturbances to the interface caused by the measurement itself. The proposed technique is indirect in that it does not require the introduction of a probe to deform the interface making it noninvasive. The viability of the technique is demonstrated through comprehensive fluid dynamics modeling of the flow involving a gas-liquid interface with different rheological behaviors.