Optical rheometry of complex fluid interfaces

Monolayers and other thin films can be rheologically complex with highly nonlinear material properties, such as shear thinning surface shear viscosities, complex moduli with both real and imaginary components, and surface normal stress differences. These responses are related to couplings between the interfacial microstructure and flow that cause distortion and alignment of the molecular and mesoscale constituents comprising the film. To understand these phenomena, and to provide the necessary background for the development of microstructural constitutive models for interfacial rheology, optical methods can provide important measurements of in situ, flow-induced structural responses.