Experimental studies of the deformation of a synthetic capsule in extensional flow

Abstract

Experiments are described to study the motion and deformation of a synthetic, liquid-filled capsule that is freely suspended in hyperbolic extensional flow. The capsule is a composite particle consisting of a viscous liquid drop surrounded by a thin polymeric membrane. The method used to fabricate capsules suitable for macroscopic flow experiments is described. The deformation of the capsule is measured as a function of strain rate for an extensional flow generated in a four-roll mill. The data agree well with results from small-deformation theory developed by Barthes-Biesel and co-workers, provided the deformation of the capsule is not too large. Using the theory to correlate the experimental data produces an estimate for the elastic modulus of the membrane that agrees reasonably well with the elastic modulus obtained by an independent technique. However, for sufficiently large strain rates, the membrane exhibits strain hardening and a permanent change in its structure, both of which are reflected in the shape of the capsule.

Large deformation of red blood cell ghosts in a simple shear flow

“…The immersed boundary node moves at this velocity for one time step to a new position given by (10) The forces exerted by the moving boundary have changed from the previous time step due to its new configuration. The new forces are calculated and the procedure is repeated to advance the flow one time step.…”

“…8 The average deformation of a suspension of red blood cells was most recently measured by Mazeron et al 9 Chang and Olbrecht have measured the deformation of a single synthetic cell whose membrane is viscoelastic in extensional and Couette flows. 10,11 The flow of deformable RBCs through capillaries can be considered axisymmetric under appropriate conditions and has been studied theoretically. Zarda et al 12 used a membrane model with a finite dilation modulus and resistance to bending stresses, and simulated axisymmetric flow through capillaries using the finite element method.…”

Deformation of a Capsule in a Spinning Drop Apparatus

“…The theoretical analysis of the deformation of a capsule 1 To whom correspondence should be addressed.…”

A counter-rotating Couette apparatus to study deformation of a sub-millimeter sized particle in shear flow

“…Subsequently, deformation of red blood cells in shear flow was investigated with a transparent counter-rotating plate-cone viscometer. 2 Recently, deformation of synthetic polymeric capsules was measured in elongational flow 3 and shear flow 4 with a four-roll mill and a counter-rotating Couette apparatus, respectively. All experiments, except those with red blood cells, were carried out with particle dimensions on the order of 1 mm.…”