Shear induced deformation of microcapsules: shape oscillations and membrane folding

The synthesis of microcapsules for technical, cosmetic and pharmaceutical a pplications has gained much interest in recent years. The design of new cap sules requires a profound knowledge of their mechanical properties. Rheolog ical studies provide important information on intrinsic membrane features, and they can also be used to develop microcapsules with tailor-made release characteristics. In this publication we used polyamide and polysiloxane mi crocapsules as simple model systems for detailed studies of fundamental the ological properties. The mechanical features of the enclosing shell materia l were analyzed in terms of a theoretical model recently proposed by Barthe s-Biesel. It turns out that this model could successfully explain the shear induced deformation and orientation process of microcapsules during flow. In addition to these fundamental studies we observed two dynamic effects: a shape oscillation and a membrane folding phenomenon. The sinusoidal fluctu ations were discussed on the basis of an existing numerical simulation. The shear induced membrane folding was not described in literature before, but besides microcapsules it could also be observed for flat membranes. (C) 20 01 Elsevier Science B.V. All rights reserved.