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The effect of different metal ions including K + , Na + , Mg 2+ , and Ca 2+ at different concentrations on the self-assembly of chitosan molecules deposited on the new cleaved mica sheet was investigated using atomic force microscopy imaging techniques and other affiliated offline analysis methods. Chitosan molecules self-assembled porous film first when combined with K + , Na + , or Mg 2+ ions, and then gradually fractured a granular structure with increasing concentration of metal ions. Chitosan molecules would be self-assembled to fibrous structure after adding calcium ions, and grew much thicker and more flat when the concentration increased. The investigations on the effects of metal ions on the self-assembly of chitosan molecules would be useful for food preservation, environmental protection, and pharmaceutical developments and industries.

The well-organized chitosan film on mica surface has drawn wide attention for its potential applications and studies on the process of self-assembly. In this article, atomic force microscopy was used to investigate the ultrastructure of the self-assembly of chitosan molecules with calcium ions in different concentrations. It was showed that calcium ions might affect the selfassembly of chitosan to a certain extent, and chitosan molecules gathered from fibrils to circular, and finally formed to film with the increasing concentration of calcium ions. Further, the formation mechanism of Ca(II)chitosan conjugates was adapted to explain the effects of calcium ions on the self-assembly of chitosan. These results and the related analysis would be valuable for guiding the pattern of chitosan self-assembly with a potential application in food packaging science and engineering. ARTICLE HISTORY