Molecular Dynamics Insights into Surfactant-Regulated Methane Hydrate Nucleation and Growth: Comparative Roles of Sodium Oleate and Hydroxylated Sodium Oleate

Natural gas hydrates, a promising solution for clean energy utilization and advanced gas storage, face significant challenges in controlled formation due to their inherently slow formation kinetics. This study employs molecular dynamics simulations to unravel the regulatory roles of sodium oleate (SO) and hydroxylated sodium oleate (HSO) in methane hydrate nucleation and growth. The findings reveal that the influence of SO and HSO on the formation of hydrates is phased. The early methane bubble expansion in SO/HSO systems delays the process of hydrate nucleation, mirroring experimental observations of foaming effects. In the later stage, SO and HSO facilitate hydrate cage stabilization through hydrophobic tail embedding and cooperative three-molecule clustering, accelerating formation kinetics. Hydroxylation in HSO enhances interfacial activity by enabling tail penetration into bubbles, reducing interfacial tension, dynamically altering bubble and hydrate growth pathways, and establishing a stable methane reservoir that sustains hydrate formation in later stages. As a result, HSO achieves superior late-stage performance with higher hydrate cage numbers and exceptional occupancy (specifically, HSO-round 2 and 3), which demonstrates an enhanced methane storage capacity. By advancing molecular-level control over hydrate nucleation and stability, this work provides a foundation for optimizing gas storage technologies and designing tailored surfactants to meet specific hydrate formation and stabilization requirements.