Long-range hydrodynamic effect due to a single vesicle in linear flow

Abstract

Vesicles are involved in a vast variety of transport processes in living organisms. Additionally, they serve as a model for the dynamics of cell suspensions. Predicting the rheological properties of their suspensions is still an open question, as even the interaction of pairs is yet to be fully understood. Here we analyse the effect of a single vesicle, undergoing tank-treading motion, on its surrounding shear flow by studying the induced disturbance field δ V , the difference between the velocity field in its presence and absence. The comparison between experiments and numerical simulations reveals an impressive agreement. Tracking ridges in the disturbance field magnitude landscape, we identify the principal directions along which the velocity difference field is analysed in the vesicle vicinity. The disturbance magnitude is found to be significant up to about 4 vesicles radii and can be described by a power law decay with the distance d from the vesicle δ V ∝ d −3/2 . This is consistent with previous experimental results on the separation distance between two interacting vesicles under similar conditions, for which their dynamics is altered. This is an indication of vesicles long-range effect via the disturbance field and calls for the proper incorporation of long-range hydrodynamic interactions when attempting to derive rheological properties of vesicle suspensions.

Numerical Study of a Confined Vesicle in Shear Flow at Finite Temperature

“…[26], which comprises both thermal membrane undulations and thermal noise [26], is adopted here to perform a detailed study of a confined vesicle in shear flow at finite temperature. The results of this model yielded very good agreement with experimental results in describing the collision process of two vesicles [19] and the flow field of a single vesicle in shear flow [27]. The system is studied in two dimensions at fixed shear rate in a wide range of the Peclet number Pe -the ratio of the shear rate to the rotational diffusion coefficient -, differently from other theoretical and numerical studies where Pe = ∞.…”