Mechanism of water diffusion into noncrosslinked and ionically crosslinked chitosan membranes

Ionically crosslinked chitosan membranes were prepared and their swelling behaviour was analysed. Low‑molecular pentasodium tripolyphosphate (TPP) and/or high‑molecular sodium alginate (NaAlg) were used as ionic crosslinkers. Dynamic swelling of noncrosslinked (Ch) as well as singly (Ch/TPP, Ch/NaAlg) and doubly (Ch/NaAlg/TPP) crosslinked chitosan membranes was performed in buffered aqueous solutions of various pH to determine the mechanism of water diffusion into these hydrogels. It was stated out that mechanism of water diffusion into studied chitosan hydrogel membranes depends both on pH of swelling solution as well as on the type of membrane (type of crosslinker). The water transport mechanism was determined to be: i) Fickian or ‘Less Fickian’ diffusion, ii) non‑Fickian diffusion (anomalous diffusion) and iii) Case II or Super Case II diffusion.