Polyelectrolyte Complex Gel with High pH-Sensitivity Prepared from Dextran Sulfate and Chitosan

摘要

Swelling equilibria of polyelectrolyte complex gels composed of dextran sulfate and chitosan were studied in dilute NaOH or HCl solutions of various pH values with or without NaCl. The complex gel with approximately equal concentrations of sulfate and amino groups was found to be highly sensitive to the change in external pH in a narrow alkaline range. The maximum equilibrium volume of the complex gel was observed at pH 10.5 and was about 300 times as large as the initial one. Compared with the swelling equilibria of a complex gel prepared from k-carrageenan and chitosan with approximately equal concentrations of sulfate and amino groups, it is suggested that the initial high density of the ionizable functional groups as well as the flexibility of acidic polymer chain contributes to the high pH sensitivity. THe increase in ionic strength of the external solution caused the decrease in gel volume and the shift of the pH value at which the maximum swelling occurred. The shift of the pH value was shown to be understood in terms of the change in the internal pH.