Robust superhydrophobic Poly(vinylidene fluoride) membranes with spherulitic surface morphology against wetting and scaling in membrane distillation

Membrane distillation (MD) offers a theoretically complete interception of salts, presenting a promising desalination pathway for freshwater supply. However, conventional hydrophobic membranes fail to desalinate water containing surfactants or supersaturated gypsum over prolonged periods. To address wetting and scaling challenges, we developed a superhydrophobization methodology for poly (vinylidene fluoride) membranes by in situ controlling spherulitic surface morphology through thermally induced phase separation. The major advantages of this one-step strategy lie in its fluorination-free, template-free, and nanoparticle-free. The as-prepared membranes exhibit a rough morphology and superhydrophobic characters with high air-trapping pockets. They demonstrate stable vapor fluxes and high salt rejections (>99 %) when used in desalination processes for saline water containing 0.6 mM sodium dodecyl sulfate , 0.03 mM cetyltrimethylammonium bromide, or gypsum solution with a saturation index of 1.1. Also, the outstanding anti-wetting and anti-scaling properties were demonstrated using synthetic shale gas wastewater. The formation of an air layer on the integrated spherulitic surface highlights the local kinetic barrier and slippery surface, effectively preventing the attachment of amphiphilic surfactants and mineral ions. Importantly, due to the membrane's structural integrity, the spherulitic surface displays high robustness and minimal impact from abrasion cycles and ultrasonication . This work exemplifies a facile strategy to engineer micro-/nano-spherulitic surface morphology for robust superhydrophobic membranes used in MD desalination.