Surfactant-induced wetting and fouling behavior in different membranes during direct contact membrane distillation

This study systematically investigated the effects of three representative surfactants, SDS (anionic), DTAC (cationic), and Brij L23 (nonionic), on membrane wetting and fouling in DCMD using PVDF, PTFE, and omniphobic membranes. These surfactants were chosen because they represent the major classes with distinct headgroup chemistries and charge states, allowing comprehensive evaluation of electrostatic, hydrophobic, and micellar interactions. Results showed that PVDF membranes experienced severe wetting and fouling, particularly with Brij L23, while omniphobic membranes maintained strong anti-wetting performance and minimal fouling. ATR-FTIR and SEM analyses confirmed surfactant penetration and fouling layer formation on PVDF, in contrast to the clean porous structures of omniphobic membranes. XDLVO calculations indicated that Lewis acid-base interactions were the dominant driving force, and membranes with higher interfacial energy barriers exhibited better fouling resistance. This study uniquely integrates counterion effects with mechanistic insights while systematically evaluating different surfactant categories and membrane types, thereby establishing a novel framework for the rational design of fouling-resistant membranes in sustainable water treatment.