Deformation of an elastic capsule in a microfluidic T-junction: settling shape and moduli determination

Abstract

Microdevices involving a stagnation-point flow, such as cross- and T-junctions, are useful for particle manipulation and characterization. In contrast to the wide use of cross-junctions, T-junctions have received limited attention as a medium for capsule deformation and characterization. In the present study, we investigate computationally the settling shape of an elastic capsule in a T-junction microchannel for a wide range of flow rates. Our work reveals that the capsules show a rich deformation behavior including (inverse) swallow-cap, sit-on and whitewater kayak shapes. We also propose a new methodology for the simultaneous and accurate determination of the shear and area-dilatation moduli of the membrane of artificial capsules via a single experimental technique by utilizing the dependence of the settling capsule’s dimensions on the capillary number and the membrane hardness identified in our investigation. Our moduli methodology utilizes high flow rates (i.e., large capsule deformations) where the effects of the membrane hardness become prominent and thus capsules with different area-dilatation modulus can be identified. Our procedure has the additional advantage of not being influenced by the fluids’ viscosity ratio or the membrane viscosity.