An omniphobic slippery membrane with simultaneous anti-wetting and anti-scaling properties for robust membrane distillation

Robust omniphobic membranes with simultaneous anti-wetting and anti-scaling properties have been developed for membrane distillation (MD) processes by means of (1) heat-pressing the electrospun nanofibrous membranes at 170 degrees C for 15 min with a light force and (2) dip coating the membranes with a low-concentration Teflon AF 2400 solution. The resultant omniphobic slippery (OMNI-SLIP) MD membrane displayed high CAs towards various liquids including water (148.41 +/- 1.50 degrees), glycerol (143.13 +/- 2.39 degrees), ethylene glycol (EG) (134.16 +/- 1.76 degrees), silicone oil (117.02 +/- 2.47 degrees), toluene (112.67 +/- 2.46 degrees) and ethanol (101.75 +/- 4.56 degrees), and a low sliding angle (10.79 +/- 1.63 degrees) towards water. The OMNI-SLIP membrane not only showed stable MD performance in wetting experiments with the presence of up to 0.4 mM sodium dodecyl sulfate (SDS) for 90h but also retarded the CaSO4 scaling due to the combinative effects of the re-entrant structure provided by electrospun nanofibers and the low surface energy offered by the Teflon AF2400 coating. Detailed mechanisms about the improved wetting and scaling resistance have been elucidated. This study may provide useful insights for material and structural design of MD membranes to treat wastewater with a complex composition.