Research on the influence of biosurfactants on wettability of 1/3 coking coal based on molecular dynamics

To improve the dust suppression effect of coal mine spray and effectively address the problems of poor degradability and environmental pollution of common chemical surfactants, based on the green and environmentally friendly characteristics of biosurfactants, this study takes 1/3 coking coal as the research object and systematically investigates the influence mechanism of three biosurfactants (lipopeptide, rhamnolipid, and sophorolipid) on its wettability. Materials Studio software was used to construct the surfactant-aqueous solution interface model and the surfactant-aqueous solution-coal ternary adsorption system. Key parameters such as the number of hydrogen bonds, radial distribution function, electrostatic potential distribution, and interaction energy were calculated via molecular dynamics simulation. Meanwhile, sedimentation experiments, contact angle measurements, and surface tension tests were carried out to evaluate the wettability of surfactants from multiple perspectives. The results show that rhamnolipid forms the largest number of hydrogen bonds with water molecules (41), and the peak of the radial distribution function between its head group and water is the highest (the first peak is at 0.097 nm), indicating its optimal hydrophilicity and interfacial activity; the surface tension of rhamnolipid solution is the lowest (28.37 mN/m); the maximum positive and negative electrostatic potentials of rhamnolipid are 0.114 60 a.u. and −0.114 61 a.u. (1 a.u. ≈ 27.211386 eV), respectively, both higher than those of water molecules, moreover, the absolute value of its interaction energy with 1/3 coking coal is the largest (−16 950 kcal/mol, 1 kcal = 4.1868 kJ), suggesting that rhamnolipid can form a more stable adsorption layer at the coal-water interface and effectively bridge the coal surface and the aqueous phase; when the mass fraction of rhamnolipid is 0.04%, the coal dust sedimentation time is the shortest (2.85 s) and the contact angle is the smallest (39.2°), with wettability significantly superior to that of lipopeptide and sophorolipid. Both molecular simulation and experimental data confirm that rhamnolipid exhibits better wetting effect on 1/3 coking coal.