The molecular dynamics study of evaporation characteristics of n-butanol-water solution on rough substrate surfaces

The evaporation behavior of self-rewetting fluids on microstructured surfaces holds critical significance for microfluidic chips and high-efficiency thermal management technologies. However, the synergistic mechanisms between substrate topography and fluid composition remain inadequately elucidated in existing studies. This investigation systematically explores the evaporation dynamics of n-butanol-water droplets on pillar-patterned rough substrates with varying geometries through molecular dynamics simulations. To decipher the influence of morphological parameters, we constructed four substrate types with distinct aspect ratios (h/l = 0.25, 0.5, 0.75, 1.0. For the optimal aspect ratio, three characteristic dimension groups were comparatively modeled (h = a, l = 2a; h = 2a, l = 4a; h = 3a, l = 6a). The evaporation mechanisms and molecular kinetics were analyzed through quantitative evaluation of vaporized molecule counts, intermolecular interaction forces, and n-butanol molecular trajectories. The results show that when the h/l of the rough substrate is 0.5, the evaporation number of the droplet is the highest, and the number of evaporated molecules increases by 12.77 %, 24.66 %, and 22.08 % compared to h/l = 0.25, 0.75 and 1. This optimized geometry promoted superior uniformity in the trajectories of n-butanol molecules. Further dimensional optimization under h/l = 0.5 revealed that the h = 2a, l = 4a configuration achieved 39.48 % and 43.46 % higher evaporation rates compared to h = a, l = 2a and h = 3a, l = 6a systems. Molecular trajectory analysis shows that the movement of n-butanol molecules is less constrained under the specific size micropillar structure, which corresponds to the other observed.