Molecular dynamics simulation of gas-liquid interface characteristics of trisiloxane and hydrocarbon surfactant mixed water-based foams

• SDS/GT-248 composite solution has synergistic effect on foam performance. • Simulated SDS and GT-248 behavior at foam’s gas–liquid interface. • SDS and GT-248 form a stable mixed layer, enhancing foam stability. • Excessive SDS interacts with GT-248, reducing foam stability. This study delves into the characteristics and synergistic mechanism of the polyether-modified trisiloxane surfactant GT-248 and the hydrocarbon surfactant SDS at the gas–liquid interface, and for the first time, utilizes molecular dynamics simulations to reveal their microscopic structure and interaction mechanism at this interface. Experimental results demonstrate that when SDS and GT-248 are mixed in a 1:1 ratio, the foam stability is significantly enhanced, with the foam half-life reaching its peak at a mass fraction of 0.16%. Further simulation analysis revealed that SDS initially forms a foundational interface at the air–water interface, followed by the aggregation of GT-248 and its hydrophobic siloxane components above the SDS layer, collectively constituting a mixed interface. This mixed layer stabilizes the foam by enhancing the interactions between SDS and GT-248 molecules, where the siloxane head of GT-248 interacts with the hydrophilic chain of SDS. At the same time, the methyl groups of GT-248 are arranged into a tight protective layer. However, if the proportion of SDS is too high, it will disrupt this mixed layer structure, weaken the intermolecular interactions, and consequently reduce the foam stability.