TY - JOUR
T1 - Vesicle dynamics in large amplitude oscillatory extensional flow
AU - Lin, Charlie
AU - Kumar, Dinesh
AU - Richter, Channing M.
AU - Wang, Shiyan
AU - Schroeder, Charles M.
AU - Narsimhan, Vivek
N1 - Funding Information:
This work was funded by the National Science Foundation (NSF) through grant CBET PMP 1704668 for C.M.S. and by a PPG-MRL Graduate Research Fellowship from the Illinois Materials Research Lab and A.T. Widiger Fellowship for D.K.
Publisher Copyright:
©
PY - 2021/12/25
Y1 - 2021/12/25
N2 - Although the behaviour of fluid-filled vesicles in steady flows has been extensively studied, far less is understood regarding the shape dynamics of vesicles in time-dependent oscillatory flows. Here, we investigate 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). Results from single vesicle experiments are found to be in good agreement with BI simulations across a wide range of parameters. Our results reveal three distinct dynamical regimes based on vesicle deformation: pulsating, reorienting and symmetrical regimes. We construct phase diagrams characterizing the transition of vesicle shapes between pulsating, reorienting and symmetrical regimes within the two-dimensional Pipkin space defined by and. Contrary to observations on clean Newtonian droplets, vesicles do not reach a maximum length twice per strain rate cycle in the reorienting and pulsating regimes. The distinct dynamics observed in each regime result from a competition between the flow frequency, flow time scale and membrane deformation time scale. By calculating the particle stresslet, we quantify the nonlinear relationship between average vesicle stress and strain rate. Additionally, we present results on tubular vesicles that undergo shape transformation over several strain cycles. Broadly, our work provides new information regarding the transient dynamics of vesicles in time-dependent flows that directly informs bulk suspension rheology.
AB - Although the behaviour of fluid-filled vesicles in steady flows has been extensively studied, far less is understood regarding the shape dynamics of vesicles in time-dependent oscillatory flows. Here, we investigate 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). Results from single vesicle experiments are found to be in good agreement with BI simulations across a wide range of parameters. Our results reveal three distinct dynamical regimes based on vesicle deformation: pulsating, reorienting and symmetrical regimes. We construct phase diagrams characterizing the transition of vesicle shapes between pulsating, reorienting and symmetrical regimes within the two-dimensional Pipkin space defined by and. Contrary to observations on clean Newtonian droplets, vesicles do not reach a maximum length twice per strain rate cycle in the reorienting and pulsating regimes. The distinct dynamics observed in each regime result from a competition between the flow frequency, flow time scale and membrane deformation time scale. By calculating the particle stresslet, we quantify the nonlinear relationship between average vesicle stress and strain rate. Additionally, we present results on tubular vesicles that undergo shape transformation over several strain cycles. Broadly, our work provides new information regarding the transient dynamics of vesicles in time-dependent flows that directly informs bulk suspension rheology.
KW - boundary integral methods
KW - capsule/cell dynamics
KW - microfluidics
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U2 - 10.1017/jfm.2021.885
DO - 10.1017/jfm.2021.885
M3 - Article
AN - SCOPUS:85119184281
SN - 0022-1120
VL - 929
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
M1 - 2021885
ER -