Berkeley Fluids Seminar

University of California, Berkeley

Bring your lunch and enjoy learning about fluids!

December 10, 2014

Dr. Joanna B. Dahl (Chemical Engineering, UC Berkeley)

Observation of Asymmetric Instability of Intermediate-Reduced-Volume Vesicles in Extensional Flow

Vesicles provide an attractive model system to understand the deformation of living cells in response to mechanical forces. These simple, enclosed lipid bilayer membranes are suitable for complementary theoretical, numerical, and experimental analysis. A recent study (Narsimhan, Spann, and Shaqfeh. in J. Fluid Mech. 750: 144-190, 2014) predicted that intermediate-aspect-ratio vesicles break up asymmetrically in extensional flow. Upon infinitesimal perturbation to the vesicle shape, the vesicle stretches into an asymmetric dumbbell with a cylindrical thread separating the two ends. In this work, we present preliminary results from cross-slot, microfluidic experiments observing this instability. The onset of breakup depends on two non-dimensional parameters: reduced volume (a measure of vesicle asphericity) and capillary number (ratio of viscous to bending forces). We will present vesicle formation protocols and image-analysis strategies for accurately measuring these quantities in order to plot a stability diagram. In particular, we will describe our synthesis of floppy, intermediate-reduced-volume vesicles and our measurement of their bending moduli by analyzing membrane thermal fluctuations. A preliminary phase diagram for asymmetric breakup will be reported.

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