The physical properties of suspensions such as emulsions and foams can be strongly affected by the presence of small particles that adsorb onto liquid-liquid or liquid-gas interfaces. This project will explore how the presence of adsorbed particles, their composition, and the arrangements they can take on an interface, which is called their mesostructure, can influence the rheology of the interface. An interfacial rheometer has been developed for this study, which will allow investigators to measure characteristics of the interface and simultaneously observe particles at the interface. The results will be used to determine the role of mesostructures on interfacial rheology. This relationship between structure and rheology is important, because many manufacturing chemical processes found in consumer cosmetics, food products, drug delivery applications, and enhanced oil recovery use emulsions that have particle-laden or particle-covered interfaces. The information gathered in this project will be useful to scientists and engineers who formulate such products and design large-scale processes to manufacture them. The investigators will use results from the project to develop a series of informative and engaging modules that can be used by instructors to teach fluid dynamics principles to university and middle-school students.
The mesostructure in particle-laden interfaces are affected by interparticle forces, which depend on composition. The mesostructure resists flow-induced deformation, resulting in an interfacial viscoelasticity. The nature of particle interactions on an interface differs from that in the bulk, primarily because of an anisotropic capillary attraction between interfacial particles. Using the interfacial rheometer, investigators will characterize the role of composition on the equilibrium mesostructure of particle-laden interfaces, characterize the role of composition on the rheology and mesostructure of deforming interfaces, and relate changes in composition such as particle surface concentration, particle size and polydispersity, and surfactant concentration to interparticle forces and viscous forces. Viscoelasticity of such interfaces affects dynamical behavior of emulsions, including drop deformation, coalescence and breakup. Understanding the relationship between composition and rheology will allow practitioners to tailor interfaces and engineer materials with desired properties.
