Stimulated aggregation, rotation, and deformation of magnetite-filled microcapsules in external magnetic fields

Microcapsules are nowadays applied in a wide range of products including food, pharmaceuticals, and cosmetic formulations. Because of their pronounced viscoelastic properties, polymer microcapsules are able to undergo mechanical deformations when they are stimulated by external signals. The elongation of capsule membranes, up to bursting processes, is important for the controlled release of active ingredients under well-defined conditions. Their application as quick and reliable control release systems affords a detailed knowledge of their rheological and mechanical properties. The aims of our work were to prepare new types of magnetic switchable microcapsules and to investigate their deformation behavior in externally imposed magnetic fields. The magnetic sensitivity was achieved by encapsulating magnetic magnetite (Fe₃O₄) particles within a polyorganosiloxane capsule. We investigated the dynamic response of those capsule suspensions and single capsules to external magnetic forces where aggregation processes, rotational movements, and field-induced deformations in static or rotating fields were observed.