Ice-Unfrozen Water on Montmorillonite Surface: a Molecular Dynamics Study

The ice-water phase transformation process and its composition distribution in frozen soil at the microscale remains unclear. The molecular dynamic (MD) simulation method was employed to study the phase transformation mechanism of water-ice on montmorillonite (Mt) surface at supercooled temperature (230 similar to 270 K). The interfacial, structural, and dynamic properties of Mt-ice-water system were discussed. The evolution of unfrozen water content with temperature in MD simulation was compared with previous results from NMR experiments for validation. The simulation results showed that 1) the transformation degree of ice into unfrozen water was almost unchanged in 230 similar to 260 K, while significantly increased when the temperature rose from 260 to 270 K. 2) The surface effect of montmorillonite played an essential role in the existence of unfrozen water in frozen soil, where coulomb electrostatic interaction was the main influencing factor. 3) Total hydrogen bonds in Mt-water-ice system could be broken due to thermal fluctuations of atoms when the temperature gradually rose. 4) The order of liquidity for the three zones was zone iii (quasi-liquid water) > zone i (bound water) > zone ii (ice).