(343f) Vesicle Shape Stability in General Linear Flows

The dynamics of vesicles in simple shear or extensional flows have been extensively studied, but the conditions where vesicles would experience in more complex flow types, such as those seen in microfluidic devices or industrial processing conditions, warrants greater investigation. In this study, we used the boundary element method to investigate the stability of moderately deflated vesicles in a general linear flow (i.e., linear combinations of extensional and rotational flows). We modeled the vesicles as a droplet with an incompressible interface with a bending resistance. We simulated a range of flow types from purely shear to extensional at viscosity ratios ranging from 0.01 to 5.0 and reduced volumes from 0.60 to 0.70. A surprising result is that the vesicle’s viscosity ratio appears to play a minimal role in describing the droplet shape and stability for many mixed flows, even in cases when significant flows are present in the vesicle interior. We also find that the critical capillary number in mixed flows collapse onto similar values, as long as the capillary number is scaled by an effective extensional rate. These results are very different than what is observed for liquid-filled systems (droplets, capsules), and we discuss the physics behind these observations in this talk. Interestingly, our simulations seem to suggest that as long as the flow type is not close to pure shear flow, one can accurately quantify the shape and stability of vesicles in a wide range of flow types by using the results from pure extension.