Fabricating Janus membranes via physicochemical selective chemical vapor deposition

Abstract

Membranes with asymmetric wettability-Janus membranes-have recently received considerable attention for a variety of critical applications. Here, we report on a simple approach to introduce asymmetric wettability into hydrophilic porous domains. Our approach is based on the physicochemical-selective deposition of polytetrafluoroethylene (PTFE) on hydrophilic polymeric substrates. To achieve selective deposition of PTFE, we inhibit the polymerization reaction within the porous domain. We prefill the substrates with glycerol, containing a known amount of free radical inhibitor, and utilize initiated chemical vapor deposition (iCVD) for the polymerization of PTFE. We show that the glycerol/inhibitor mixture hinders the deposition of PTFE within the membrane pores. As a result, the surface of the substrates remains open and porous. The fabricated Janus membranes show stable wetting-resistant properties, evaluated through sessile drop contact angle measurements and direct contact membrane distillation (DCMD).

Advances in surface modification and functionalization for tailoring the characteristics of thin films and membranes via chemical vapor deposition techniques

“…As discussed in the previous sections, this might be due to the fact that essentially CVD derivative techniques have emerged to suit different pressure ranges and thus, each process works at certain range of associated pressure. Nevertheless, in a study, Ghaleni et al 172 studied the effect of deposition pressure on membrane contact angle. They came into the conclusion that increasing the pressure during the iCVD coating can have a moderate effect on the contact angle of hydrophobic PTFE‐modified PVDF membrane evidenced by its ~20% increase upon changes in pressure from 300 to 1200 mTorr.…”

“…The state of decline in water flux during the operation as an indication of stability of deposition for a few CVD‐modified MD membranes 171–173,175,180 . [Color figure can be viewed at wileyonlinelibrary.com]…”

Surface and Interface Engineering of Polymer Membranes: Where We Are and Where to Go

“…In some research, one side of the hydrophilic membranes or fabrics is exposed to the fluorinated silanes for gradient hydrophobic modification . Similarly, the hydrophobic membrane can be also asymmetrically hydrophilized through a single-sided CVD or ALD process. − For example, Tufani and Ozaydin Ince deposited different polymers on each side of an AAO membrane by iCVD . On the other hand, Waldman et al applied the single-sided ALD to deposit the hydrophilic inorganic layer (Al 2 O 3 ) on a polymer membrane (PP) .…”

“…150 Similarly, the hydrophobic membrane can be also asymmetrically hydrophilized through a single-sided CVD or ALD process. 151 on each side of an AAO membrane by iCVD. 152 On the other hand, Waldman et al applied the single-sided ALD to deposit the hydrophilic inorganic layer (Al 2 O 3 ) on a polymer membrane (PP).…”

Hydrolysis of Poly(fluoroacrylate) Thin Films Synthesized from the Vapor Phase

“…Due to their hydrophobicity, fluoropolymer thin films are difficult to synthesize using traditional methods, so this discussion of film surface chemistry non-uniformity will be limited to polymer chemical vapor deposition (CVD) techniques (in-depth discussion of polymer CVD will follow). The existing polymer CVD research focuses on three main applications of in-plane surface chemistry non-uniformity: Janus membranes, − templated (or patterned) surfaces, − and chemical gradients. − Janus membranes are valuable in applications such as membrane distillation, water collection in arid environments, breathable fabric for activewear, and wound dressings with improved blood barrier and wound protection properties. , Templating is used to produce patterns of two contrasting chemistries, which may be used for drug release, biosensors, and artificial skins. − Films with chemical gradients have been used to mimic in vivo cellular growth conditions. − …”