Omniphobic surface modification of electrospun nanofiber membrane via vapor deposition for enhanced anti-wetting property in membrane distillation

Membrane distillation (MD) is a promising technology for treating saline industrial wastewater, but current hydrophobic MD membranes suffer significant wetting issues due to contaminants commonly present in wastewater. In this study, we report an effective method to fabricate a polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) electrospun nanofiber membrane with improved anti-wetting property against low-surface-tension substances. Without surface activation, the pristine electrospun nanofiber PVDF-HFP membrane with intrinsic re-entrant structure was directly fluorinated by 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (FDTS) employing vapor deposition (VD). The fluorinated membrane exhibited excellent surface omniphobicity with high water and ethanol contact angle of 154.1 ± 0.1° and 122.6 ± 1.7°, respectively. The fluorinated membrane showed highly stable omniphobicity and mechanical properties at harsh conditions such as ultrasonic, boiling water, acid and base treatment. More importantly, the resultant omniphobic membrane exhibited robust wetting resistance to the saline feed containing sodium dodecyl sulfate (SDS, 0.4 mM) in an 8-h dynamic direct contact MD (DCMD) test. This study provides an effective and benign approach to fabricate omniphobic nanofiber membranes which have great potential in treating saline wastewater containing low surface tension substances.