8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P9.33Dynamics and rheology of vesicle suspension in shearflowAntonio Lamura 1 and Gerhard Gompper 21 IAC CNR, Via Amendola, 122/D, 70126, Bari, Italy2 ICS FZ Juelich, Juelich, GermanyWe consider a two-dimensional suspension of deflated vesicles under shear flow at finite temperaturefor different concentrations. The system is simulated in a hydrodynamic solvent by usingthe multi-particle collision technique. First we analyze the interaction of two vesicles in the tanktreadingregime. They slide over and around each other increasing their vertical separation afterscattering with strong fluctuations of vesicle shape and inclination angle. This result is in goodquantitative agreement with experimental results. The dependence of the suspension intrinsic viscosityon the viscosity ratio between inner and outer fluids, λ, is found to be monotonic with λ atthe fixed outer fluid viscosity for λ in dilute and semi-dilute regimes. The behavior of concentratedsuspensions is even more interesting being characterized by a shear thinning behavior since the intrinsicviscosity decreases with the shear rate over more then one decade for different values of λ.Moreover, there is also a clear indication of the formation of vesicle-free boundary layers of finitethickness, ∆, next to the system walls. ∆ increases with the shear rate reaching saturation. Whenincreasing the system width, the values of ∆ grow as also observed in two-dimensional simulationsof red blood cells in small vessels. Finally, it is found a non-linear dependence of ∆ on λ withthe boundary layer decreasing at high values of the viscosity contrast attaining a maximum at thetank-treading to tumbling transition.33