An NMR relaxation study of the state of water in gelatin gels

A combination of H-1 and Na-23 NMR is used to probe the dynamic state of wa ter in gelatine gels as the water content is lowered from 70% to dryness. A sharp increase in the proton and sodium transverse relaxation rates is obs erved as the water content falls from 20 to 15% while the proton longitudin al and dipolar cross relaxation rates show a maximum at ca, 15%. We show th at these observations can be understood if monolayer coverage occurs at 15% and multilayers of less strongly interacting hydration water are formed be tween 15 and 20%. Above 20% the water appears to behave as an unperturbed b ulk phase, (C) 1999 Academic Press.