Influence of SiO2 nanoparticles grafted with surfactant on coal wetting properties and microscopic mechanism of action

Context

In coal mine spray dust suppression, conventional studies on individual surfactants or surfactant mixtures often fail to achieve optimal coal wettability enhancement. This study innovatively introduces SiO₂ nanoparticles and demonstrates through simulations that the nanoparticle-surfactant composite system substantially enhances coal wettability. Electrostatic potential analysis indicates that the modified nanoparticle molecules formed by surfactant-grafted nanoparticles are more likely to form stable structures with coal molecules, enabling the nanoparticles to be better fixed on the coal molecules and establish a stable adsorption configuration. When the surfactant-grafted composite structure adsorbs onto the coal surface, it significantly enhances water molecular diffusivity, facilitates increased hydrogen bond formation with the composite surface, and substantially strengthens the interaction energy between coal and surfactants. Moreover, nanoparticle incorporation leads to noticeable thickening of the coal wetting layer and a marked increase in water molecule density at the interface. The results conclusively demonstrate that this composite structure enhances coal wettability through three synergistic mechanisms: interface optimization, hydrogen bond reinforcement, and water molecule diffusion enhancement.

Methods

This study innovatively employed molecular dynamics simulation methods to construct two adsorption systems—“water-surfactant-coal” and “water-nanoparticle-grafted surfactant-coal”—based on the Wiser coal molecular model. Through comprehensive analysis of key parameters including adsorption configurations, interaction energies, relative concentration profiles, hydrogen bond counts, water molecule diffusion behaviors, and detailed examination of surface electrostatic potentials of various components, we conducted comparative studies on the wetting behaviors of sodium dodecyl sulfate (SDS), alcohol ethoxylate (AEO₉), and their nanoparticle-composite systems on coal. This investigation successfully revealed the microscopic mechanism by which composite structures enhance coal wettability at the molecular level.