Macro-corrugated and nano-patterned hierarchically structured superomniphobic membrane for treatment of low surface tension oily wastewater by membrane distillation

Understanding the fouling/scaling resistance of superhydrophobic/omniphobic membranes in membrane distillation

“…11 shows slightly more complicated procedure to prepare hierarchical nanostructures membrane with omniphobicity [46,117]. Either incorporation of the silica nanoparticles to the nanofibers [46] or attached to the positively charged surface [117], the final membrane demonstrated fouling resistance to SDS or scaling resistance, which was mainly attributed to the slippage surface. Because the irregular surface pattern, the evaluation of the wetting state was difficult.…”

“…Measurement of the slip length has not yet been reported. However, from the experimental results of the sliding angles [45,46,74,117],…”

A Critical Review of Membrane Wettability in Membrane Distillation from the Perspective of Interfacial Interactions

“…On the basis of the value of ζ, the wetting state could be divided into Wenzel (or pinned) wetting (ζ > 0.75), transition state (0.75 > ζ > 0.50), and Cassie (−Baxter) (or suspended) state (ζ < 0.50). A low value of ζ for modified omniphobic membranes (<0.5) , confirmed their Cassie state due to air pockets.…”

“…The region at the wetting frontier near the water–air interface plays an important role in the wetting behavior induced by a surfactant (Figure C). Complete wetting could be observed for commercial membranes (e.g., PVDF, PVDF-HFP, and PTFE) in the presence of sodium dodecyl sulfate (SDS) even at a low concentration (<29 mg·L –1 ), ,,− and CA reached 0° within 7 s for the wetted membrane . A superhydrophobic PVDF membrane also showed partial wetting for 0.1–0.2 mmol·L –1 SDS, while an omniphobic membrane was able to resist wetting for SDS up to 0.3–0.4 mmol·L –1 . − Surfactant-induced wetting depends on surfactant type and concentration, as well as type and concentration of salts in the feed, caused by the difference in surface tensions, hydrophilic–lipophilic balance, and critical micelle concentration. ,, Depending on surfactant type, the presence of salt (e.g., NaCl or NaNO 3 ) could delay (e.g., 2-EHS or sodium dodecyl benzene sulfate (SDBS)) or accelerate wetting (e.g., SDS). , Nonionic surfactant (e.g., Tween 80) or cationic surfactant (e.g., TDAB) lead to more severe membrane wetting compared to anionic surfactant (e.g., SDS), , which is probably because of the attractive force between the cationic surfactant and negatively charged membrane surface.…”

“…Unlike waters that contain surfactants, oily wastewater could result in severe fouling in MD process without affecting the permeate quality. ,, No wetting of composite PVDF membrane modified with SiO 2 nanoparticles (SiNPs), together with polydopamine or chitosan, occurred during filtration of a crude oil mixture (1000 mg·L –1 ) . However, the membranes were eventually wetted when surfactant (100 mmol·L –1 Triton X-100) was added to the crude oil-in-water emulsion .…”