Microcapsules for controlled release via donnan dialysis

The preparation of ion-exchange microcapsules that exhibit a diameter of 10 40μm, a membrane shell of 0.1-1μm in thickness and with charge densities in the range of 0.8-1.2 meq/g is described. The microcapsules were prepared by interfacial cross-linking of bromomethylated poly(phenylene oxide) (PPOBr) and poly(ethyleneimine) (PEI). These polymers were dissolved in toluene and aqueous solutions, respectively. Upon dispersing the PEI solution in the organic phase, ion-exchange microcapsules were instantaneously formed. These microcapsules contain aqueous solutions of PEI and inorganic salt and are self-sealing. They can be dried and stored in a “dormant”, inactive state. Upon exposure to ambient humidity or aqueous solutions, water diffuses rapidly into the microcapsules, establishing the conditions for Donnan exchange of ions between the external phase and the microcapsule interior. Some preliminary transport measurements of the exchange of encapsulated nitrate ions (a corrosion inhibitor) with chloride ions (a corrosion inducer) in the external phase via a Donnan exchange mechanism are reported. Ion transport and leakage rates are compared with those obtained from flat sheet ion-exchange membranes made from identical materials.