Reorientation dynamics of water and ice in partially crystalline gelatin-water mixtures

We combine 2H nuclear magnetic resonance (NMR) with broadband dielectric spectroscopy (BDS) to investigate reorientation dynamics of water and ice in partially crystalline 30 and 45 wt. % gelatin-water mixtures. For water, NMR and BDS correlation times agree and follow an Arrhenius law with an activation energy of Ea ∼ 0.55 eV with no evidence of a dynamical crossover in the temperature range 140-270 K for either concentration. Analyses of NMR correlation functions with varied angular resolutions show that water reorientation is quasi-isotropic and involves large-angle jumps even in the partially crystallized states. For ice, NMR and BDS consistently yield Ea ∼ 0.47 eV below 250 K. This activation energy differs from typical values of bulk hexagonal ice but agrees with those reported for ice in various other mixtures and confinements. NMR correlation functions decay in a mildly stretched manner to a residual correlation of F∞ ∼ 1/7. We attribute the stretching to a stacking disorder of ice in the gelatin mixtures. Moreover, the value of the residual correlation shows that all molecular orientations in the crystal structure are explored, and hence, that the observed reorientation process involves translational jumps of the molecules.