The viscoelastic behaviour of chitosan was followed by dynamic mechanical analysis (DMA) while the
sample was immersed in gradient compositions of water/ethanol mixtures. The swelling equilibrium
of chitosan membranes, both crosslinked with genipin or not, increased linearly with the water content.
Increasing the water content, it was simultaneously observed a peak in the loss factor (around 25 vol.%)
and a reduction of the storage modulus, which was attributed to the a-relaxation of chitosan. This was
the first time that the glass transition dynamics in a polymer was monitored in immersion conditions
where the composition of the plasticizer in the bath is changed in a controlled way. The water content
at which tan d presented a maximum increased with both increasing frequency and increasing crosslinking
density. The permeability decreased steadily with the ethanol content, reaching very low values
around the glass transition. Therefore we hypothesize that conformational mobility of the polymeric
chains may play an important role in the diffusion properties of molecules trough polymeric matrices.