Stretching of capsules in an elongation flow, a route to constitutive law. (20th February 2015)

• Record Type: Journal Article
• Authors: de Loubens, C.; Deschamps, J.; Boedec, G.; Leonetti, M.
• Is Part Of: Journal of fluid mechanics. Volume 767(2015:Mar.)
• Publication Date: 2015-02-20
• Subjects: biological fluid dynamics, -- capsule/cell dynamics, -- low-Reynolds-number flows; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2015.69
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Soft bio-microcapsules are drops bounded by a thin elastic shell made of cross-linked proteins. Their shapes and their dynamics in flow depend on their membrane constitutive law characterized by shearing and area-dilatation resistance. The deformations of such capsules are investigated experimentally in planar elongation flows and compared with numerical simulations for three bidimensional models: Skalak, neo-Hookean and generalized Hooke. An original cross-flow microfluidic set-up allows the visualization of the deformed shape in the two perpendicular main fields of view. Whatever the elongation rate, the three semi-axis lengths of the ellipsoid fitting the experimental shape are measured up to 180 % of stretching of the largest axis. The geometrical analysis in the two views is sufficient to determine the constitutive law and the Poisson ratio of the membrane without a preliminary knowledge of the shear elastic modulus $G_{s}$ . We conclude that the membrane of human serum albumin capsules obeys the generalized Hooke law with a Poisson ratio of 0.4. The shear elastic modulus is then determined by the combination of numerical and experimental variations of the Taylor parameter with the capillary number.