Deformation of single emulsion drops covered with a viscoelastic adsorbed protein layer in simple shear flow

The small-deformation behavior of single Newtonian oil drops covered by an adsorbed viscoelastic protein layer is investigated in simple shear flow. Adsorption and network formation of the protein (lysozyme) at the oil/water interface are tracked by interfacial rheology and tension. While uncovered drops deform to the expected steady ellipsoidal shape, protein-covered drops are able to resist the bulk shear stress to a much higher degree, leading to a smaller average deformation and oscillating drop shapes. The results show direct evidence for a commanding role of in-plane interfacial stresses of a viscoelastic protein network on the macroscopic drop deformation as opposed to the equilibrium interfacial tension.