Fig. 4
From: Trade-off in membrane distillation with monolithic omniphobic membranes
Mechanism underlying wetting resistance-water vapor permeability trade-off in MD desalination with monolithic omniphobic membranes. a, b Schematics (not drawn to scale) showing that the effective water–air interfacial area for evaporation (solid green line) increases when feedwater wets the pores. c Cross-sectional view of PVDF membrane surface, with the pore larger than the critical pore size for wetting (i.e., wetted pore depicted in blue). The scale bar represents 2 μm. d The positive correlation observed between area fraction of wetted pores and the initial water vapor flux of the membranes. Error bars represent standard deviation from three independent measurements. e, f A series of snapshots from numerical simulations, showing dynamic formation of e nonwetted and f wetted pores on omniphobic membrane (Pb ≈ 1.8 kPa > Pa ≈ 1.2 kPa for the first layer) and hydrophobic membrane (Pb ≈ 1.19 kPa < Pa ≈ 1.2 kPa for the first layer), respectively. Water cannot permeate through the second layer because Pb (~29.4 and ~19.5 kPa for the second layer of omniphobic and hydrophobic membranes, respectively) was greater than Pa. Note that Pa refers to applied pressure. Pb refers to breakthrough pressure, which can be estimated using Eq. (1)
