The Effect of Spacer Chain Length on Foam Stability of Mixed Amine Gemini Surfactant/NaOl by Molecular Dynamic Simulations

Foam stability critically determines the efficiency of the mineral flotation process. Although the mixed amine Gemini surfactant/anionic surfactants exhibit excellent flotation performance, atomic-level investigations of the mechanism of their impact on foam stability remain limited. This study employs molecular dynamics simulations to investigate the self-aggregation behavior of mixed amine Gemini surfactant/sodium oleate (NaOl) systems with varying spacer chain lengths at the air/water interface. The structural parameters of self-aggregation, surface tension, synergistic energy, and diffusion coefficient of water molecules were calculated in detail. The results of molecular dynamics simulations indicated that synergistic adsorption between surfactants occurred. Compared with single amine Gemini surfactant systems, the mixed surfactant systems exhibited an enhanced interfacial activity. The spacer chain length significantly affected the adsorption configurations of the mixed surfactant at the air/water interface. For spacer chains containing fewer than five methylene groups, carboxyl groups preferentially adsorbed between two intramolecular amine groups, forming independently clustered aggregates. Conversely, longer spacer chains promoted adsorption between carboxyl groups and intermolecular amine groups, forming interconnected network-like aggregates. Both structural configurations constrained interfacial water mobility, thereby reducing the liquid flow rate between foam films, suppressing water loss and enhancing the mechanical stability of flotation foams.