Deformation of a capsule in simple shear flow:: Effect of membrane prestress -: art. no. 072105

We investigate the effect of an initial isotropic prestress on the mechanics of a spherical capsule freely suspended in a simple shear flow. The capsule consists of a drop of liquid enclosed by a very thin hyperelastic membrane. A sufficient prestress may prevent the buckling instability that arises at low shear rates when the membrane bending resistance is neglected. A small perturbation analysis of the capsule deformation is first obtained for small prestress and weak viscous stresses. When the viscous shear stress and the preinflation are large, a numerical model of the capsule deformation shows how prestress decreases the capsule deformation for a given shear rate and how it significantly increases the elastic tension in the membrane at a given deformation level. These results may help the experimentalists to detect the presence of an osmotic pressure difference in a semipermeable capsule. (c) 2005 American Institute of Physics.