Solution interactions with omniphobic PVDF/SiO₂/FAS-17 membrane in membrane distillation by molecular dynamics simulation approach: Impact of surfactant, oil, and ions

Membrane distillation is a promising technology for desalination and wastewater treatment but is limited by wetting and fouling, particularly in oily saline solutions. This study investigates the interactions between an omniphobic polyvinylidene fluoride (PVDF) membrane and multicomponent feed solutions using molecular dynamics (MD) simulations and direct contact membrane distillation (DCMD) experiments. 10ns MD simulations were performed to explore the behavior of two representative surfactants - anionic Sodium dodecyl sulfate (SDS) and cationic Dodecyltrimethylammonium bromide (DTAB) - chosen due to their opposite charges and widespread use. The surfactants interacted with a fluorinated SiO2 surface mimicking the membrane coating. Results showed that SDS exhibited higher adsorption in saline environments, increasing the risk of wetting, whereas DTAB displayed delayed but more persistent adsorption. The presence of hexane alone reduced surfactant-surface interactions; however, in the presence of NaCl, adsorption increased significantly, indicating a complex interplay between feed components and membrane surface chemistry. DCMD experiments confirmed that the omniphobic PVDF membrane maintained high salt rejection and stable flux while minimizing wetting and fouling. The close correlation between simulation and experimental data demonstrates the predictive power of MD modeling for membrane-foulant interactions, guiding the rational design of membrane surfaces and feed formulations to enhance long-term DCMD performance.