Regulation behavior and mechanism of hydrophilic groups of dodecyl surfactants on wetting of gas-bearing coal

Gas and coal dust are the two major killers that restrict coal mine safety production and endanger the lives and health of miners. Coal seam water injection was widely used for coal dust prevention and gas control. However, in coal seams with high gas content interferes with the wetting of coal by moisture, resulting in poor wetting effect of gas-bearing coal. Dodecyl surfactants (C₁₂H₂₅-HG) were frequently utilized in studies aimed at enhancing the wetting of non-gas-containing coal. Typical hydrophilic groups (HG) within these surfactants include -OH, -COOH, and -SO₃H. However, the regulatory behavior and mechanisms of these groups concerning the wetting of gas-containing coal remain unclear. This paper conducted research using experimental and molecular dynamics simulation methods. The surface tension between C₁₂H₂₅-HG solution and gas, the contact angle between C₁₂H₂₅-HG solution and gas-containing coal, the interfacial energy, the evolution of functional groups after C₁₂H₂₅-HG solution and pure water infiltration of coal samples, and the potential difference between hydrophobic sites and water molecules showed that the control effect of -OH, -COOH, and -SO₃H hydrophilic groups on the wetting of gas-bearing coal gradually increased. In the micro models of surfactant solutions and gas-bearing coal, the interactions between -OH, -COOH, and -SO₃H hydrophilic groups and oxygen atoms in water molecules are enhanced, and their radial distribution functions and coordination numbers gradually increase. The presence of hydrophilic groups such as -OH, -COOH, and -SO₃H results in an increasing radial distribution function and coordination number between hydrophobic groups and coal molecules. For dodecyl surfactant solutions containing -OH, -COOH, and -SO₃H groups, the adsorption degree of water molecules gradually increases and the diffusion coefficient gradually decreases, while the aggregation degree gradually increases. The degree of methane molecule displacement gradually increases and the diffusion coefficient gradually increases. The introduction of - SO₃H hydrophilic groups into the solution helps to improve the wetting performance of gas-bearing coal. The research results provide theoretical guidance for efficient screening of surfactants suitable for coal mine gas control and revealing the mechanism of injecting surface active water into coal seams for gas control.