Orientation and Dynamics of a Vesicle in Tank-Treading Motion in Shear Flow

Experimental results on mean inclination angle and its fluctuation due to thermal noise in tank-treading motion of a vesicle in shear flow as a function of vesicle excess area, normalized shear rate, viscosity, and viscosity contrast between inner and outer fluids, ϵ, are presented. Good quantitative agreement with theory made for ϵ=1 was found. At ϵ>1 the dependence is altered significantly. Dependence of the vesicle shape on shear rate is consistent with theory. A tank-treading velocity of the vesicle membrane is found to be a periodic function close to that predicted by theory.