Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We investigated a miscible displacement of a less viscous liquid by a more viscous shear-thinning liquid in a Hele-Shaw cell. Due to a coacervation interaction between both liquids, a hydrodynamic instability appears in the form of inward viscous fingering. The liquids consisted of a solution of the anionic biopolymer xanthan gum, as the injection liquid, which displaced a cationic C14T AB aqueous solution. In the contact zone between the two solutions, the oppositely charged species form polymer-surfactant complexes due to electrostatic interactions. These complexes are insoluble in water and separate from the aqueous solution in the form of a gel-like growing membrane. During the continuing radial displacement, a large variety of patterns can emerge which is attributed to the rheological properties of the system involving viscosity gradients, the non-Newtonian nature of the displacing solution and the complex rheology of the coacervate phase. Variation of the flow rate and gap width of the Hele-Shaw cell revealed distinct instability regimes and allowed to identify main contributing mechanisms. These insights open the door for further investigation of fluid mechanics (i.e. Saffman-Taylor instability), pattern formation and self-organization problems in multiphase systems of complex rheology and its applications in engineering and technology.