Water migration driven by temperature gradients in confined clay channels

• A combined model of kaolinite channels and water molecules was built. • The microstructure of water molecules in confined channels of kaolinite was investigated. • The migration ability of water molecules in the confined channels of kaolinite was quantified. • The temperature gradient, channel surface properties and ambient temperature have multiple effects on the migration of water. Frost heave is primarily caused by the formation of ice lenses, which is heavily influenced by water migration driven by temperature gradients. However, the molecular mechanisms underlying water migration in soil nanochannels under temperature gradients remain unclear. In this paper, molecular dynamics simulations were used to study the microstructural characteristics of water molecules, as well as the effects of temperature gradients and nanochannel wettability on water migration in confined clay channels. The results show that water migration is significantly influenced by the interplay of temperature gradient, ambient temperature, and channel surface properties. As the temperature gradient increases, water molecules migrate toward the colder region, with migration peaking at the gradients between 1.2 K/nm and 1.8 K/nm. Beyond this range, reducing atomic activity at lower temperatures limits water mobility. Hydrophilic surfaces interact with water molecules more strongly, promoting the formation of more hydrogen bonds and hourglass-like structures. Notably, single-sided hydrophilic nanochannels achieve water migration distances approximately 8.27 times greater than those of double-sided hydrophilic nanochannels, with a corresponding 6.75-fold increase in the driving force generated by temperature gradients. In contrast, double-sided hydrophobic nanochannels exhibit negligible water migration due to insufficient driving forces. This work offers a molecular-level understanding of the mechanisms driving water migration in frozen soils.