Desalination, Vol.466, 36-43, 2019
Scaling mitigation in membrane distillation: From superhydrophobic to slippery
Scaling is a major obstacle to commercial application of membrane distillation (MD) for desalination. Contemporary understanding of scaling formation onto hydrophobic membrane was built on thermodynamic assumption of a non-slip condition. This research provides an alternative theory and a novel insight from a hydrodynamic view of slip boundary. We purposely selected three polyvinylidene difluoride (PVDF) membranes with different surface characteristics - namely a tailor made superhydrophobic micro-pillared (CF4-MP-PVDF), a micro-pillared (MP-PVDF) and a commercial (C-PVDF) membranes, for direct contact membrane distillation (DCMD) using a supersaturated CaSO4 feed. MD flux analysis showed that CF4-MP-PVDF was highly scaling resistant whereas the other two membranes were not. Nucleation energy barrier, wetting state factor and slip length were used to explain for the observed difference in scaling behavior. Results showed that hydrodynamic properties, such as the wetting state and slip length, play a critical role in determining the anti-scaling behavior of a hydrophobic membrane rather than the contact angle nor the thermodynamic nucleation energy barrier. New findings from this study serve as a new guideline for the fabrication of antiscaling membranes by creating a slippery surface.