Mechanistic understanding of Triton X-100 and SDBS adsorption on mineral surfaces: An experimental and simulation study

The efficiency of chemical enhanced oil recovery (EOR) is significantly influenced by the adsorption behavior of surfactants on rock surfaces, a phenomenon not fully understood in terms of molecular structuring and interfacial dynamics. In this study, we present a multi-scale investigation that integrates static adsorption experiments, quartz crystal microbalance with dissipation (QCM-D), and molecular dynamics (MD) simulations to elucidate the adsorption characteristics of two representative nonionic and anionic surfactants, Triton X-100 and sodium dodecyl benzene sulfonate (SDBS). Their adsorption capacities followed the order: montmorillonite > calcium carbonate > silicon dioxide. The adsorption isotherm of surfactants on calcium carbonate and silicon dioxide followed the Langmuir model, while adsorption on montmorillonite aligned more with the Freundlich model. Kinetic studies indicated that the adsorption processes for both surfactants followed the pseudo-second-order model. Thermodynamic analysis revealed that the adsorption processes were both exothermic and spontaneous. Notably, QCM-D measurements further confirmed bilayer adsorption structures for both surfactants at the solid-liquid interface. Complementary MD simulations provided molecular-level insights into adsorption energy, conformational arrangement, spatial distribution, and hydrogen bonding networks, revealing distinct interaction mechanisms for the two surfactants. The obtained results offer a comprehensive understanding of surfactant-rock interactions, which are crucial for optimizing chemical flooding processes in EOR applications.