Wetting characteristics and driving mechanism of droplets on bituminous coal surface

The key to coal dust capture is the interface effect generated when the droplets come into contact with the coal dust particles. To clarify how the interfacial structure drives the wetting process of droplets on the bituminous coal surface, droplet deposition was selected to conduct macroscopic wetting experiments, and Newtonian mechanics was applied to implement microscopic molecular dynamics simulations. Investigate the wetting effects of droplets of different volumes on the bituminous coal surface, explore the causes of driving force differences, and examines the droplet’s driving mechanism. The findings elaborate on the wetting characteristics of droplets on bituminous coal surfaces and reveal the driving mechanisms of the solid-liquid interface wetting process. The main conclusions are as follows: at the millimeter scale, the droplet-driven wetting process on the bituminous coal surface is more easily influenced by capillary forces. Reducing droplet volume can increase the capillary driving force, thereby accelerating the transition rate through the “inertial force-driven–capillary force-driven–static equilibrium” three-stage process, allowing the droplet to complete the wetting process more rapidly. An inverse correlation exists between droplet volume and interfacial wetting performance: as the droplet volume decreases, the contact angle at the solid-liquid interface reduces, the mobility of water molecules becomes more restricted, and their tendency to adsorb onto bituminous coal molecules increases, resulting in a more uniform coverage of the wetted region and a more stable interfacial wetting effect. The difference in driving effect caused by droplet volume can be explained from an energy perspective. In the initial state, water molecules are only influenced by non-bonded interactions with each other, resulting in similar average cohesive energy among water molecules. As the wetting phase begins, the average cohesive energy of water molecules within smaller droplets decreases, while the number of hydrogen bonds per unit area at the interface increases. This driving mechanism of droplets on the bituminous coal surface, at the macroscopic level, is characterized by the advancement and stagnation of the contact line, allowing the water droplets to adhere to the bituminous coal surface. Microscopically, part of the water molecules at the droplet’s interface edge forms a precursor film on the coal surface, and water molecules actually migrate along this film. Ultimately, equilibrium is achieved under the combined influence of the droplet’s intrinsic cohesive energy and interfacial binding energy. In dustproof applications, small-size droplets can achieve uniform wetting more quickly, while large-size droplets are suitable for larger coverage and continuous wetting scenarios.