Thermal and NMR investigation of the change in the states of water caused by volume phase transition of gelatin gel

The occurrence of volume phase transition (VPT) of a polymer gel is often accompanied by the loss of water. In view of the fact that few studies have been made on the change in different states of water during VPT, in this paper, DSC and NMR are used to check the variation in states of water during VPT of glutaraldehyde crosslinked gelatin gel caused by the variation in composition of water-acetone mixture. The results indicate that the volume of gel collapses at 50% acetone concentration. The contents of free, intermediate and bound water absorbed by gelatin gel decrease with an increase in the amount of acetone. At 50% and 60% acetone content, free water disappears; because acetone accounts for 70% and 85%, there remains only bound water. Near VPT the relative content of bound water to total water increases sharply. The spin-lattice relaxation times (T-1) determined by NMR show that the T-1 values of intermediate and bound water, respectively, decrease by approximately four and ten times compared with that of free water. Before VPT, most of the water is freezable and highly mobile. After VPT, bound water gradually plays a dominant role in the mobility of water in the gel. The findings are helpful in understanding the dehydration process of protein induced by poor solvent. (C) 2000 Society of Chemical Industry.