Aqueous foam is widely used in fire extinguishing and dust suppression technologies. Improving the foaming ability is the key to reducing the added concentration of foaming agents as well as the economic cost. In this work, the effect of a water-soluble polymer (polyvinyl alcohol, PVA) on the foaming ability of anionic surfactant (sodium dodecyl ether sulfate, SDES) was studied by an experiment and molecular dynamics simulation. The experimental results showed that PVA greatly improves the foaming ability of SDES solutions when the surfactant concentration is less than 0.1%, which is attributed to the fact that the polymer can enhance the stability of bubble films and reduce the bubble rupture rate during the foam generation process. The simulation results indicate that PVA can enhance the hydration of surfactant head groups and contribute to the formation of a three-dimensional hydrogen bond network between surfactants, polymers, and water molecules, thus greatly improving the stability of bubble liquid films. The above results suggest that water-soluble polymers can be used to improve the foaming ability of surfactant solutions by enhancing the bubble film stability, which is beneficial as it reduces the added concentration of foaming agents in aqueous foam applications.

Surfactants are often used in the process of coal dust suppression, and the wetting effect is greatly affected by the surfactant hydrophilic group structures. In order to explore the influence of hydrophilic groups of surfactants on their adsorption states and wetting effect on coal dust, three surfactants with similar hydrophilic groups were selected, namely, anionic surfactant sodium dodecyl sulfate (SDS), anionic-nonionic surfactant alkyl ether sulfate (AES), and nonionic surfactant alkyl polyoxyethylene ether-3 (AEO-3). To assess surfactant efficiency, surface tension, wetting time, infrared spectra, and wetting heat were analyzed. These parameters provide insights into molecular adsorption, interfacial behavior, and energy changes during wetting. The different adsorption states of surfactants on the coal dust surface due to EO and SO₄²⁻ hydrophilic groups were analyzed. Results show that both anionic surfactant SDS and nonionic surfactant AEO-3 form the monolayer adsorption structure on the coal dust surface. Due to the electrostatic repulsion of SO₄²⁻ groups, the adsorption density of SDS is lower than that of AEO-3, which results in the higher wetting heat of AEO-3 compared to SDS. In addition, the EO groups without electrostatic repulsion make AEO-3 molecules more tightly adsorbed at the air–liquid interface, causing the minimal surface tension. Therefore, the wetting time of AEO-3 is shorter than that of SDS. The anionic-nonionic surfactant AES has both EO and SO₄²⁻ groups. Because the EO groups in the inner surfactant adsorption layer can attract Na⁺ ions to distribute around them, the free AES molecules further form the outer adsorption layer under the electrostatic attraction between SO₄²⁻ groups and Na⁺ ions. The double-layer adsorption structure causes the hydrophobic groups of the outer AES molecules to face outward, the hydrophobic sites on the coal dust surface are not completely transformed into hydrophilic sites. Although AES exhibits the highest adsorption density, it has the lowest wetting heat and the longest wetting time. The research results can provide theoretical guidance for the selection of suitable surfactants for coal dust suppression.

Water-soluble polymers are often used as additives to adjust the foam properties of surfactant. In this study, the effects of water-soluble polymer poly(ethylene oxide) (PEO) on foam properties of two anionic surfactants, i.e., ammonium lauryl ether sulfate (ALES) and sodium dodecyl sulfate (SDS), were investigated by experimental and molecular dynamics simulation methods. Experimental results show that the addition of PEO can reduce the foaming ability of the two surfactants, but the inhibitory effect of PEO on the foaming ability is weakened at high surfactant concentration. Compared with ALES, PEO has a more significant inhibitory effect on the foaming ability of SDS. With the increase in PEO concentration, the half-life time of foam drainage in surfactant/water-soluble polymer composite systems gradually increases. The synergistic effect between PEO and ALES is stronger than that between PEO and SDS, resulting in a longer half-life time of foam drainage in ALES/PEO composite system. Molecular dynamics simulation results indicate that the addition of PEO can decline the air–water interface thickness of bubble films and the tail tilt angle of surfactant molecules at the air–water interface. The reduction in tail tilt angle means that the surfactant molecules are more vertical to the air–water interface and the hydrophobic interaction between adjacent tail chains of surfactants is weakened, which is unfavorable to the formation of bubble films, thus decreasing the foaming ability of surfactants. Because the ALES/PEO system has larger air–water interface thickness and surfactant tail tilt angle than the SDS/PEO system, the inhibitory effect of PEO on the foaming ability of ALES is weaker than that of SDS. Adding PEO can lower the peak position of the first hydration layer of surfactant head groups, increase the number of hydrogen bonds, and reduce the diffusion coefficient of water molecules, so that the surfactant/water-soluble polymer system has longer half-life time of foam drainage than the pure surfactant system. Due to the synergistic effect between ALES and PEO, the ALES/PEO system has a higher peak value of the first hydration layer of surfactant head groups, more hydrogen bonds, and lower diffusion coefficient of water molecules than the SDS/PEO system. Therefore, the half-life time of foam drainage in the ALES/PEO system is longer than that in the SDS/PEO system.