Chitosan Derivatives/Calcium Carbonate Composite Capsules Prepared by the Layer-by-Layer Deposition Method II Stabilization of the Shell by Crosslinking

The layer-by-layer deposition method is utilized to prepare rodlike core/shell capsules. Chitosan (polycation) and chitosansulfate (polyanion) were alternatively deposited on the surface of calcium carbonate whisker (rodlike particle). The thickness of the obtained shells ranged from 26 to 42 nm. After the deposition, the shell was treated with diisocyanate to form crosslink between the chitosan or chitosansulfate chains in order to stabilize the deposited shell. The obtained shell crosslinked rodlike capsules were successfully converted to hollow particles by immersing them into hydrochloric acid due to the enhanced shell stability, whereas from noncrosslinked shells, no hollow capsules were yielded: the shell was removed by dissolution in hydrochloric acid. It is revealed that the crosslinking reactivity is higher for 1,6-diisocyanatehexane than for tolylene 2,4-diisocyanate, suggesting that the reactivity depends on the size and flexibility of the crosslinking molecule.