DYNAMIC WATER-ABSORPTION CHARACTERISTICS OF CHITOSAN-BASED HYDROGELS - AN INVESTIGATION BY POSITRON-ANNIHILATION LIFETIME SPECTROSCOPY

The water content dependence of the free volume in chitosan-based hydr ogels was studied using the positron annihilation lifetime spectroscop y (PALS) technique. The dynamic water absorption behavior was correlat ed with the variation in the mean lifetime (tau(3)) and intensity (I-3 ) Of the o-Ps component. PALS data suggest that water clusters coexist with individual water molecules at the beginning of swelling. The com parison between the calculated and measured values of tau(3) and I-3 i mplies that the free volume of the hydrogel network has a great effect on the state of water.