(18c) Nonlinear Hydrodynamics of Sheared Protein Drops in Microgravity

The presence of macromolecules such as proteins significantly affects fluid motion of the air-liquid interface through adsorption and molecular conformation. This sensitive response establishes the air-liquid interface as a unique boundary for fluid flows. The role of the air-liquid interface is further accentuated in microgravity due to the prominence of surface tension in the absence of gravity. Results will be presented showing velocity measurements along with rheological modeling of protein solutions in microgravity and on Earth. The ring-sheared drop (RSD) operating aboard the International Space Station (ISS) serves as a microgravity biochemical reactor, consisting of a one inch diameter liquid drop contained by surface tension alone and pinned between two contact rings. One ring rotates to impart interfacial shear that is transmitted via surface shear viscosity to produce inertially-enhanced mixing of the bulk fluid. The combination of inertia in the bulk flow and a non-Newtonian interface leads to a nonlinear coupled flow. Experiments with multiple protein types across a range of concentrations are compared with COMSOL simulations.