Emulsion Drops with Complex Interfaces: Globular Versus Flexible Proteins

This study focuses on the flow behavior of emulsion drops with complex interfaces. The experimental approach includes three different length scales: (i) interfacial rheology is discussed for adsorbed proteins with different molecular structure (compact and globular for beta-lactoglobulin versus flexible and random coil for beta-casein); (ii) the flow of single drops with macromolecular adsorption layers is studied using optical flow cells; (iii) dilute emulsions are investigated using rheology and rheo-small angle light scattering (rheo-SALS). Different hydrodynamic models for drops with and without interfacial viscoelasticity are assessed. For the case of rigid interfacial layers, a comparison with capsule suspension models suggests that drops stabilized by adsorbed particles or globular proteins behave like soft capsules surrounded by a jammed shell. Their behavior on the single drop level is similar to the mechanics of red blood cells or vesicles.