Synthetic capsule break-up in shear flow

Abstract

A capsule, a thin elastic membrane enclosing inner material such as colloid, has been used in diverse fields including drug delivery, cell encapsulation and cosmetics. The hydrodynamic shear stress acting on the membrane surface of the capsule in microcirculation environment may cause severe deformation and burst of the capsule. Though, many studies have focused on the rheological behavior of the capsule immersed in various flows, little is known for the deformation of a capsule in high shear rate and furthermore its break-up phenomenon. For the break-up of a capsule in simple shear flow, experiment is performed with a Couette flow rheoscope, and a capsule based on Human Serum Albumin is prepared. The membrane of the capsule is modelled as a thin shell with Hookes law. The deformation and the break-up of a capsule and the resultant stress distribution on the capsule surface are investigated with varying the shear rate of the flow. Two kinds of the observed break-up are presented, which occur at the intermediate shear rate and the high shear rate. The break-up at high shear rate is related to the tear-up of the membrane at the meridional plane after the material yields. On the other hand, a periodic tank-treading accompanies the cyclic stess acting on the membrane which is found to be correlated to the fatigue of the membrane and results in the tip separation in the intermediate shear rate.