NMR OF ABSORBED SYSTEMS .2. A NMR STUDY OF KERTIN HYDRATION

The proton magnetic resonance spin-spin and spin-lattice relaxation times of water absorbed by wool keratin at different levels of water absorption have been measured as a function of the temperature in the range -65 to 50°C. Results are consistent with the absorbed water being described in terms of a continuous distribution of nuclear correlation times. An analysis of this data according to the Odajima-Resing theory for such a system resulted in physically reasonable values being obtained for the analytical parameters involved. It is proposed that the absorbed water exists as small clusters of no more than a few molecules, even near saturation absorption. By assuming an Eyring thermal activation law to govern the temperature dependence of the median nuclear correlation time, it was possible to closely fit the results over the experimental temperature range by this theory at all levels of absorption for which suitable data were obtained. The general application of this activation law enables the absorbed water at a given level of absorption to be denned in terms of a further two parameters-the apparent activation enthalpy and entropy. The analytical results suggest that as the level of absorption is increased, the width of the distribution of the nuclear correlation times of the absorbed water is decreased, but that there is little shift in the median correlation time of the distribution. By comparison with corresponding parameters obtained for ice, it is estimated that the average molecular reorientation time of the absorbed water is about 1000 times shorter than for water molecules in ice at 270°K.