NMR characterization of the pore structure and anisotropic self-diffusion in salt water ice

NMR imaging and one- and two-dimensional self-diffusion propagator measurem ents of the liquid phase in salt water ice are presented. The properties of the network of brine-filled pores are found to depend on the growth condit ions of the ice. Two types of samples are compared: (a) shock-frozen ice pr oduced in the probe in situ and (b) ice grown over several hours under cont rolled conditions. By shock-freezing, an ice structure could be produced wh ich featured streak-like porous channels of diameters of up to 300 mu m all owing almost unrestricted self-diffusion along one preferential axis but re duced diffusivities in the remaining directions. In ice grown under control led conditions, the pore sizes are near the resolution limit of the imaging experiment of typically 50 mu m. For this type of samples, strongly non-Ga ussian self-diffusion propagators are obtained, indicating restricted self- diffusion on rms scales of 30 mu m. Common to all samples was the observati on of highly anisotropic self-diffusion. One- and two-dimensional propagato rs are compared in order to estimate the degree of anisotropy and the size of the restrictions. (C) 2000 Academic Press.