Giant unilamellar vesicle dynamics in large amplitude oscillatory extension

The dynamics of vesicles in simple shear and extensional flows have been thoroughly studied. However, the flow types present in microfluidic devices or biological systems are not always described by those flows alone. We present our work on the nonlinear dynamics of vesicles in large amplitude oscillatory extensional (LAOE) flows using both experiments and boundary integral (BI) simulations. Our results characterize the transient membrane deformations, dynamical regimes, and stress response of vesicles in LAOE in terms of reduced volume (vesicle asphericity), capillary number (dimensionless flow strength), and Deborah number (dimensionless flow frequency). We find the results from single vesicle experiments to be in good agreement with BI simulations across a wide range of parameters. Our results reveal three dynamical regimes based on vesicle deformation: pulsating, reorienting, and symmetrical regimes. The dynamics observed in each regime result from a competition between the flow frequency, flow time scale, and membrane deformation timescale. Broadly, this work provides new information regarding the transient dynamics of vesicles in time-dependent flows that informs bulk suspension rheology. We will also present some preliminary work on the dynamics of multicomponent vesicles.