Magnetic Resonance Imaging Study of Freezing and Thawing Processes of Ice Composites Reinforced with Polymer Materials

The processes of water freezing and ice thawing were studied in hydrogels based on sodium polyacrylate, sodium alginate, carboxymethylcellulose of different degrees of crosslinking, and para-aramid hydrogels filled with water. Using magnetic resonance imaging (MRI) method the hydrogels swelling, water distribution within the para-aramid hydrogel, freeze/thaw front propagation and resulting changes in ice composites structure were visualized. It was observed that the presence of a polymer macromolecular network in ice composites based on cross-linked hydrogels hinders the size of ice crystallites formed during freezing, leaving the qualitative picture of the freezing processes unaffected. At the same time, the water-filled porous structure of the para-aramid hydrogels undergoes irreversible changes during the freezing process, which leads to the destruction of the ice composite. It was found out that the rate of freeze/thaw front propagation in ice composites based on cross-linked hydrogels depends on both the mass content of the polymer material and its crosslinking degree. The results obtained demonstrate the capabilities of MRI in studying the heat and mass transfer processes in ice composite materials, which have potential for practical application.