Molecular mechanisms of coal dust wettability: Hydrophilic group modulation for enhanced surface interactions

[Display omitted] •Determined interaction type and strength among surfactant, water, and coal.•Established a quantitative standard for surfactants to enhance coal dust wettability.•Revealed the micro mechanism of how different hydrophilic groups affect wetting. The wettability of coal dust by surfactant-regulated solutions is influenced by the hydrophilic structures of the surfactants. This study combines macro- and microscopic experiments to determine the wettability performance of four surfactants with identical hydrophobic groups but different hydrophilic groups. Through molecular simulation, a molecular-level evaluation standard for the surfactant’s impact on coal dust wettability was established. Additionally, the correlation mechanism between the electrostatic potential distribution of the hydrophilic groups and their wettability was identified. Sulfonic groups—compared with sulfate, hydroxyl, and amino groups—can more effectively enhance the solution’s wettability, reducing the solution’s surface tension to as low as 22.1 mN/m and achieving a molecular wettability area of 78.84. Furthermore, the electrostatic potential extreme of the sulfonic group was − 53.61 kcal/mol, with an electrostatic potential wettability area of 28.99 Å2. This represents an improvement of approximately 34.43 % and 5170.91 %, respectively, compared with hydroxyl groups. Greater electrostatic potential extremes and electrostatic potential wettability areas led to stronger electrostatic adsorption, more adsorbed water molecules, and better wettability of coal dust. This study provides theoretical guidance for the rational design of functional surfactants for surface engineering and pollution control applications.