Water Mobility in the Interfacial Liquid Layer of Ice/Clay Nanocomposites

At solid/ice interfaces, a premelting layer is formed at temperatures below the melting point of bulk water. However, the structural and dynamic properties within the premelting layer have been a topic of intense debate. Herein, we determined the translational diffusion coefficient D_t of water in ice/clay nanocomposites serving as model systems for permafrost by quasi-elastic neutron scattering. Below the bulk melting point, a rapid decrease of D_t is found for charged hydrophilic vermiculite, uncharged hydrophilic kaolin, and more hydrophobic talc, reaching plateau values below -4 °C. At this temperature, D_t in the premelting layer is reduced up to a factor of two compared to supercooled bulk water. Adjacent to charged vermiculite the lowest water mobility was observed, followed by kaolin and the more hydrophobic talc. Results are explained by the intermolecular water interactions with different clay surfaces and interfacial segregation of the low-density liquid water (LDL) component.