(381f) Vesicle Dynamics in Large Amplitude Oscillatory Extension, Simulations and Microfluidic Experiments

Vesicles are widely used as systems for studying cell-like dynamics, and their dynamics 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. For our first 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). Continuing with our research on single vesicle dynamics, we are performing simulations and microfluidic experiments on quasi-spherical vesicles in large amplitude oscillatory extensional (LAOE) flows. By using LAOE we can probe the non-linear extension and compression of vesicles and how these types of deformation affect dilute suspension microstructure in time-dependent flows through contractions, expansions, or other complex geometries. We model the vesicles as a droplet with an incompressible interface with a bending resistance. Our preliminary numerical results for vesicles with a viscosity ratio of 1.00 and reduced volumes from 0.80 to 0.95 have shown there to be three general dynamical regimes differentiated by the amount of stretching that occurs in each half cycle. The different dynamics are mainly due to the competition of the flow frequency and the vesicle deformation timescale. Experiments are performed in a cross-slot microfluidic device and current results show agreement for low frequency oscillations. We have additionally observed the relation between average stress and strain rate is highly nonlinear. The consequences of such rheology and the dynamical regimes will be discussed in this talk.