Joseph Zasadzinski

Expanding and contracting surfactant or protein coated liquid-liquid and liquid-vapor interfaces are ubiquitous in science and technology and play an essential role during inhalation and exhalation in the lungs and in interfacial formation of aggregates of therapeutic proteins. Surfactant adsorption and interfacial shear and dilatational rheology also influence the stability, drainage, and evolution of foams and emulsions. The elastic and viscous components of the dilatational modulus, and interfacial shear modulus, dictate how the interface responds to surface deformations, which in turn determine the magnitude of the local interfacial stress, which in turn, determines interfacial stability. For example, the dilatational and shear properties of the interface between the epithelial lining fluid and gas in the lung alveoli may determine whether the lung can expand easily and uniformly during breathing. At cellular membrane interfaces, these properties may determine cellular motility and endocytosis.

The stability of interfacial films in the eye are essential to preventing “dry-eye” syndrome and the comfort of wearing contact lenses. Interfacial shear and dilatational properties influence the flow and drainage of the borders between bubbles or drops, and hence the evolution of foams and emulsions in foods and commercial cleaning products. Methods to measure the adsorptiondilatational and shear rheology of complex fluids at interfaces require mathematical models for their interpretation. These models are often non-linear and require numerical evaluation or fits to multiple parameters. MSI resources are beneficial to developing and using mathematical models to describe experimental results.