Coupled interfacial and thermal effects on water imbibition in soil nanopores: A revised Lucas-Washburn framework based on molecular dynamics study

The classical Lucas-Washburn (LW) equation fails to accurately describe capillary imbibition phenomena in soil nanopores, where nanoconfinement, temperature, and surface charge substantially alter interfacial water behavior. A generalized form of the LW equation is proposed, which integrates nanoscale effects through a physics-informed scaling factor f. This new formulation explicitly incorporates interfacial and thermal influences that are previously treated in isolation and whose coupled effects are neglected, significantly extending the applicability of the LW model to nanoconfined soil media. Using molecular dynamics (MD) simulations across 45 representative montmorillonite slit-pore systems (2–10 nm wide, 0–104.91 cmol·kg−1 CEC, and 300–360 K), the water interfacial structure is identified via a density-based clustering algorithm (DBSCAN) and extracted imbibition slopes are used to calibrate the model through systematic analysis of the interfacial and thermal effects on capillary transport. The generalizability of the revised framework is further demonstrated through 18 additional simulations for different soil mineral systems, including kaolinite and quartz. The novel LW equation significantly enhances predictive performance, increasing the coefficient of determination from 0.19 to 0.92. Cross-mineral comparisons demonstrate its broad applicability, with R2 = 0.95 for kaolinite and 0.92 for quartz. Experimental validation using red-layer mudstone data confirms the accuracy of the proposed model, reducing RMSE from 71.63 mm to 5.54 mm. This work bridges interfacial molecular-level insights and practical continuum-scale predictions, offering a robust tool for assessing capillary-driven water transport in mineral-rich environments.