Defect-driven transition from total to partial wetting of dimethylformamide on two-dimensional hexagonal boron nitride

Structural defects can strongly modulate the wetting behavior of polar liquids on the surfaces of two-dimensional materials. In this study, molecular dynamics simulations were performed to investigate the wetting behavior of dimethylformamide (DMF) on hexagonal boron nitride (hBN) substrates containing two representative defect types: monovacancies and two-ring protrusions. The influence of defect density was systematically examined using three configurations: nanodroplets, liquid nanoplugs, and nanofilms. DMF exhibits a total-wetting behavior on pristine hBN and hBN with vacancy defects. Although increasing vacancy defect density significantly slow down the spreading kinetics, the final state remains a total-wetting state, consistent with the nanuoplug and nanofilm observations. In contrast, protrusion defects induce a transition from total to partial-wetting state once a critical protrusion density is exceeded. Beyond this threshold, the equilibrium contact angle increases monotonically, indicating enhanced hydrophobicity. Nanoplug simulations corroborate this behavior, showing a transition from an unstable liquid plug at low protrusion density to a stable plug at higher density. Density-profile analysis of the nanofilms reveals that protrusions weaken the affinity of DMF for hBN, leading to depletion of DMF molecules near the surface. Collectively, these results establish distinct mechanistic roles for vacancies and protrusions in governing DMF wetting on defect-engineered hBN.