Polyurea microcapsules: Surface modification and capsule size control

A postmodification method for polyurea microcapsule (PUMC) surfaces using functional polyelectrolytes is reported in this article. Fluorescein isothiocyanate (FITC) was used to probe the chemistry on PUMC surface and label nucleophilic groups on the surface, in particular amines. As well, a fluorescently labeled polyanion containing electrophilic acetoacetate groups was used to covalently react with these nucleophilic groups on the PUMC surfaces. This modification causes charge reversion of the originally cationic PUMC and enables subsequent layer-by-layer (LbL) coating using other polyelectrolytes, allowing for covalent or noncovalent modification of the capsule surface. All modification steps were monitored using either laser scanning confocal microscopy or fluorescence microscopy. Optical and fluorescence microscopy of PUMC wall cross-sections embedded in resin confirmed that the modifications were restricted to the outer surface of PUMCs, offering minimum interference of this modification method with other capsule wall properties. In addition, a simple T-junction type microfluidic device based on a commercially available MicroTEE was designed to produce narrowdisperse PUMCs. This device was easy to set up and operate and was proved to be an useful tool for making monodisperse emulsions and narrowdisperse MCs.