Due to solute impurities and freezing temperature depression in polycrystalline ice, a complicated and dynamic network of liquid water forms at the boundaries between solid ice crystal grains. Ice is essentially a low porosity porous media, where ice crystals compose the solid matrix and liquid veins the pore space. As ice ages, it undergoes a thermodynamically driven coarsening, termed recrystallization, whereby larger ice crystals grow at the expense of smaller ones, altering vein dimensions. Impurity concentrations, temperature and pressure influence this network structure and therefore impact physical, transport and rheological properties of ice.
However, the nature of this internal network structure is not fully understood. NMR magnetic relaxation time and molecular diffusion measurements, proven robust in probing pore structure in porous media, are sensitive to vein dimensions and therefore provide a novel method for monitoring ice structure and its evolution with time. With NMR, information on liquid water content, vein surface to volume ratios and tortuosity as a measure of vein network interconnectivity can be obtained. These measurements provide unique insight into the physical characteristics of polycrystalline ice with relevance ranging from geophysical applications in cryospheric systems to freezing processes in biotechnology applications.