Forward osmosis works on a deceptively simple principle. Water spontaneously flows from a feed solution of lower osmotic pressure toward a concentrated draw solution on the other side of a semipermeable membrane. Because the process requires no external pumping pressure, it fouls less than pressure-driven reverse osmosis and can be paired with draw solutes that are easily recovered, or run as a pretreatment stage ahead of reverse osmosis. The heart of any such system is the membrane itself, typically a thin polyamide active layer formed on a porous support. The polyamide layer is created by interfacial polymerization, in which an aqueous amine monomer, usually m-phenylenediamine, meets an organic acyl chloride monomer, usually trimesoyl chloride, at the support’s surface. The reaction is fast and self-limiting, producing an ultrathin but dense film whose thickness, roughness and crosslinking density dictate how fast water moves and how well it rejects solutes.

For years, membrane scientists have tried to tune that film by embedding nanomaterials, a approach known as thin-film nanocomposite design. Nanoparticles of zeolites, metal-organic frameworks, carbon nanotubes, graphene oxide and MXenes have all been slipped into or beneath the polyamide layer, with mixed results. Additives can create extra water pathways and increase hydrophilicity, but they can also introduce defects, agglomerate into clumps that wreck selectivity, or leach out over time. The Iranian team chose a different class of additive altogether: a polyamide-based hyper-crosslinked polymer. Hyper-crosslinked polymers are amorphous, permanently porous networks built from rigid aromatic building blocks locked together by extensive covalent crosslinks. Their high internal surface area, tunable chemistry and chemical stability have made them popular in gas storage and catalysis, and this study puts them to work as a nanofiller for water membranes.

The synthesis itself was characterized with a battery of analytical techniques. Attenuated total reflectance Fourier-transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy confirmed that the hyper-crosslinked polymer had formed successfully, revealing a layered morphology rather than a granular one. Elemental mapping of the material showed that nitrogen-bearing groups were distributed uniformly throughout the structure, a detail that matters because those amide and amine groups interact strongly with water and with the monomers used in membrane fabrication. The high nitrogen content and even dispersion suggested the polymer would integrate well into the polyamide chemistry rather than sitting inertly inside it as a foreign body.

The genuinely clever part of the study is how the polymer gets into the membrane. Rather than blending it into the support or into the aqueous monomer solution, the researchers used what they call an intermediate strategy. The hyper-crosslinked polymer was dispersed in hexane, an organic solvent in which the polymer can be spread as a coating, and that dispersion was applied to the membrane support surface precisely between the aqueous amine phase and the organic acyl chloride phase. The polymer thus occupies the very frontier where interfacial polymerization happens. As the two monomers diffuse toward each other and react, they must contend with a porous, nitrogen-rich, layered material sitting at the reaction zone. The result is a polyamide film whose growth has been sculpted from the inside out.

That sculpting shows up clearly in the membrane’s final properties. The presence of the hyper-crosslinked layer changed the dynamics of monomer diffusion and film nucleation, and the modified active layers came out smoother, thinner and more hydrophilic than films polymerized without the additive. Each of those three attributes pushes performance in the right direction. A thinner film shortens the path water must travel. Greater hydrophilicity improves wetting and reduces the energetic penalty water pays entering the polymer network. Reduced roughness matters for fouling, because contaminants preferentially snag on peaks and valleys, so a smoother surface resists the accumulation of organic matter and dye molecules during long filtration runs. Chemical characterization confirmed the hyper-crosslinked polymer was stably embedded within the polyamide matrix rather than loosely deposited on top of it.

The performance numbers are the study’s headline. An unmodified forward osmosis membrane delivered a water flux of 12.2 liters per square meter per hour, a common benchmark unit abbreviated LMH. At the optimal loading of hyper-crosslinked polymer, flux rose to 23.4 LMH, an increase of more than 90 percent. Pushing the additive loading higher actually backfired, with flux declining again because excess polymer drove the formation of a thicker polyamide layer, which added resistance faster than the extra pathways added permeability. That dose-dependent behavior is typical of nanocomposite membranes and underscores why loading optimization is the central design variable. Importantly, the modified membrane also showed enhanced specific reverse salt flux, meaning that the salt that inevitably leaks backward from the draw solution did so at a rate disproportionately low relative to the water gained, an indicator that selectivity had not been sacrificed for speed.

To test the membrane under realistic and demanding conditions, the team ran a 24-hour continuous process concentrating reactive black B, a widely used anionic dye responsible for much of the colored effluent discharged by the textile industry. The membrane rejected more than 99.9 percent of the dye throughout the run and displayed an anti-fouling tendency, resisting the flux decline that usually plagues dye concentration processes as molecules build up on the membrane surface. The authors attribute this resilience to the combination of smoothness, hydrophilicity and stable integration of the hyper-crosslinked polymer within the active layer. Sustained performance over a full day of operation is a meaningful demonstration that the additive does not wash out, degrade or progressively separate from the polyamide, concerns that have undermined other nanofiller systems.

Why does a porous polymer interlayer boost flux so dramatically? The mechanistic picture, supported by the characterization data, centers on how the intermediate layer reshapes interfacial polymerization itself. Interfacial polymerization is governed by the diffusion of monomers into the reaction zone; anything that moderates that diffusion changes the film’s architecture. The hexane-dispersed hyper-crosslinked coating likely slows the amine monomer’s transport toward the organic phase and provides abundant hydrogen-bonding and amide interaction sites, yielding a film that is simultaneously thinner and more uniformly crosslinked. Related interlayer strategies in the literature, using materials from chitosan and cyclodextrins to covalent organic frameworks and MXene-carbon nanotube assemblies, have shown similar gains, confirming that controlling the reaction frontier is one of the most powerful levers in membrane design. What distinguishes the present work is the use of a permanently porous, polymer-based network rather than an inorganic nanoparticle, which sidesteps problems of particle agglomeration and interfacial incompatibility.

The broader significance lies in what the result says about the permeability-selectivity trade-off, the长久-standing constraint that forces membrane designers to choose between fast and clean. By growing a thinner, smoother, more hydrophilic polyamide film without opening defects, the hyper-crosslinked interlayer improved water transport while preserving rejection of salts and dyes, suggesting the trade-off is not an immutable law but a consequence of how films are made. For desalination, higher flux at equal selectivity translates directly into less membrane area and lower capital cost. For textile wastewater treatment, a membrane that concentrates reactive dyes with near-total rejection and low fouling could enable water reuse and dye recovery in one of the world’s most water-intensive industries. The study, published in Polymer Bulletin with financial and instrumental support from the University of Tehran, adds a versatile new tool, a synthetically tunable porous polymer, to the membrane engineer’s toolkit, and points toward a generation of forward osmosis membranes that no longer ask designers to choose between speed and selectivity.

Subject of Research: Modification of thin-film nanocomposite forward osmosis membranes with a hyper-crosslinked polymer interlayer to enhance water flux, salt rejection and dye concentration

Article Title: Modification of thin film nanocomposite forward osmosis membranes using hyper-crosslinked polymer via intermediate strategy

Article References: Mirsaeidghazi, E., Shakeri, A., & Salehi, H. (2026). Modification of thin film nanocomposite forward osmosis membranes using hyper-crosslinked polymer via intermediate strategy. Polymer Bulletin, 83(12), Article 652. https://doi.org/10.1007/s00289-026-06710-0

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06710-0

Keywords: forward osmosis, thin-film nanocomposite membrane, hyper-crosslinked polymer, interfacial polymerization, polyamide, water desalination, dye concentration, anti-fouling, membrane modification, water flux, reverse salt flux, textile wastewater treatment

Membrane distillation is a deceptively elegant process. Instead of pushing salt water through tiny pores at high pressure, as in reverse osmosis, membrane distillation exploits a temperature difference across a hydrophobic, microporous membrane. Water vapor evaporates from the warm feed stream, travels through the air-filled pores, and condenses on the cooler permeate side, leaving salts, metals, and most dissolved impurities behind. Because the driving force is vapor pressure rather than hydraulic pressure, the method can concentrate extremely saline brines, treat produced water from oilfields, and even recover valuable resources from waste streams. Its one great vulnerability, however, lies in the word hydrophobic. Standard hydrophobic membranes resist pure water, but real-world feeds are full of surfactants, oils, alcohols, and low-surface-tension organics that can sneak into the pores, flooding the membrane and destroying the air-water interface on which the whole process depends.

The field’s answer has been the omniphobic membrane, a surface engineered to repel essentially all liquids, not just water. The trick to true omniphobicity lies in geometry as much as chemistry. Surfaces decorated with re-entrant structures, overhanging profiles that curve inward like the walls of a mushroom or a springtail’s skin texture, can trap a stable layer of air beneath low-surface-tension liquids, because the liquid cannot make contact angle progress on the undercut geometry even when its surface tension is low. Researchers have fabricated such surfaces using fluorinated silanes, sprayed nanoparticles, and hydrothermally grown nanorods. But each approach carries a cost: nanoparticles are only weakly glued to the substrate and shear away in turbulent feed flows, hydrothermal synthesis typically demands high temperatures and multiple steps, and complex layer-by-layer recipes resist scale-up beyond small membrane coupons.

The Malaysian team’s contribution is to sidestep all three problems at once with a single, scalable chemistry. Electroless deposition, a process borrowed from metallurgy and recently demonstrated on fabrics and eggshell membranes, uses a catalytic seed layer to drive crystal growth from an aqueous solution without any external electrical power. In their scheme, the polyvinylidene fluoride (PVDF) hollow fiber membranes are first sensitized with a catalyst, then immersed in a zinc salt solution where zinc oxide nucleates and grows directly on the fiber surface. Crucially, the entire process operates below 90 degrees Celsius and at ambient pressure, conditions mild enough that the polymer substrate never softens, warps, or degrades, and mild enough that continuous, roll-to-roll-style fabrication of long membrane modules becomes genuinely plausible.

The elegance of the method lies in its tunability. By simply varying the concentration of the zinc precursor, the researchers grew two distinct families of nanostructures. Dilute solutions of 0.05 molar produced rod-like protrusions, while richer solutions at 0.1 and 0.2 molar shifted the growth toward prism-type architectures. Because the crystals form in situ, anchored at their roots by the catalytic interface rather than merely sitting atop the polymer, the resulting structures resist detachment far better than dip-coated nanoparticles, which the same group had previously shown to be vulnerable to adhesion loss. That structural integration matters enormously in membrane distillation, where feed sparging, crossflow shear, and chemical fouling constantly batter the surface.

Among the membranes tested, the one grown from the intermediate 0.1 molar precursor struck the most favorable balance between roughness, pore blockage, and vapor permeability. Its surface resisted wetting by multiple low-surface-tension liquids, holding contact angles above 112 degrees even for liquids that would instantly soak a conventional hydrophobic membrane. It withstood a liquid entry pressure of 5.8 bar, a measure of how hard the feed can push before liquid forces its way into the pores, while still transporting water vapor efficiently. The lesson is that more nanostructure is not always better: excessively aggressive growth raises mass transfer resistance and shrinks effective pore size, throttling the flux that makes a desalination membrane economically viable.

Performance under realistic fouling conditions is where the new membrane truly distinguished itself. The team challenged it with direct contact membrane distillation using a saline feed spiked with humic acid, a ubiquitous natural organic matter component notorious for gluing foulants to membrane surfaces and for teaming up with salts to induce catastrophic pore wetting. Over short-term tests the optimized membrane lost only 4.6 percent of its water flux, and over a full 24-hour continuous run the decline reached just 13 percent, all while rejecting nearly 100 percent of the salt. Stable salt rejection throughout the run is the key indicator: it means the pores stayed dry, the entrained air layer held, and the liquid never breached the membrane, even in the presence of wetting-prone organic matter.

The broader significance of the work is as much about manufacturing as it is about materials science. Laboratory demonstrations of omniphobic membranes are abundant, but industrial deployment demands processes that are cheap, energy-efficient, continuous, and tolerant of the polymer substrates used in commercial hollow fiber spinning. A process that runs below 90 degrees Celsius in ordinary aqueous baths at atmospheric pressure, requiring no autoclaves, no vacuum systems, and no exotic precursors, fits the bill. The authors point out that electroless deposition can in principle be applied continuously to long lengths of hollow fiber, turning membrane modification from a batch-bound bottleneck into an in-line production step. That kind of manufacturability, they argue, is what separates a promising paper from a deployable technology.

There are, of course, questions that only longer trials will answer. Twenty-four hours of stable operation is encouraging but a far cry from the months of continuous duty expected in a plant, and the long-term durability of the fluorinated surface chemistry that typically accompanies omniphobic membranes remains an industry-wide concern. Scaling effects, feed chemistries beyond humic acid, and the economics of precursor consumption all await scrutiny. Yet the core achievement stands: a re-entrant, strongly anchored, omniphobic nanostructure grown on a flexible polymer fiber under conditions gentle enough for mass production. If desalination is to reach the hypersaline brines, oilfield waters, and industrial effluents that reverse osmosis cannot touch, membranes like these, built by chemistry simple enough to be scaled, may prove to be exactly the durable, wetting-resistant workhorses the field has been searching for.

Subject of Research: Low-temperature electroless growth of ZnO re-entrant nanostructures on PVDF hollow fiber membranes for omniphobic, wetting-resistant membrane distillation desalination.

Article Title: A low-temperature electroless route for in-situ growth of ZnO re-entrant nanostructures for scalable omniphobic hollow fiber membranes in wetting-resistant membrane distillation

Article References: Iqbal, R. M., Tai, Z. S., Othman, M. H. D., Arifin, N. D. T., Shazana, N. A., Rahman, M. A., Mustapa, W. N. F. W., Kadirkhan, F., Puteh, M. H., Jaafar, J., Rahman, M. A., & Ismail, A. F. (2026). A low-temperature electroless route for in-situ growth of ZnO re-entrant nanostructures for scalable omniphobic hollow fiber membranes in wetting-resistant membrane distillation. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13735-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13735-3

Keywords: membrane distillation, omniphobic membrane, zinc oxide, electroless deposition, PVDF hollow fiber, re-entrant nanostructures, desalination, wetting resistance, anti-fouling, water treatment, nanomaterials, membrane fabrication

The study, led by Wenjun Zhang of the Frontiers Science Center for Deep Ocean Multispheres and Earth System at Ocean University of China, together with colleagues at the University of Shanghai for Science and Technology and Shandong University, introduces what the authors call a heterogeneous wetting membrane, or heterowettability membrane. Unlike conventional membranes, which present a single uniform wettability to the fluid they contact, this membrane features spatially patterned regions of hydrophilic and hydrophobic surface chemistry arranged side by side. The design is paired with a bidirectional gradient contraction channel module, and it is this combination that allows one device to do the work of two.

The central insight of the work lies in how the two components divide their labor. The gradient contraction channel is not merely a piece of plumbing. As fluid flows through a channel whose cross-section narrows progressively, the velocity field becomes non-uniform, generating a spatially varying shear stress across the flow. That non-uniform shear field acts directly on the emulsion droplets, deforming them and gradually destabilizing the surfactant shells that keep them intact. In effect, the channel performs a gentle, continuous demulsification before the fluid ever reaches the membrane surface, priming the droplets to coalesce and release their contents at the membrane interface.

Once the partially demulsified dispersion arrives at the membrane, the patterned wettability takes over. Droplets of the dispersed phase encounter surface regions whose chemistry matches their own continuous phase affinity, and the resulting surface energy gradients drive them to migrate in opposite directions across the membrane. Water droplets in an oil continuous phase are drawn toward hydrophilic zones, while oil droplets in water are pulled toward hydrophobic zones. Coupled with the shear-induced demulsification and directional phase transport, this wettability-guided routing allows oil-in-water and water-in-oil emulsions to be processed simultaneously and in parallel, each yielding its own purified phase.

A critical challenge in any such dual-function design is preventing the two phases from crossing into each other’s collection pathways, a failure mode known as continuous phase crossover. The researchers addressed this with what they describe as a pressure field–Laplace anchoring mechanism. By carefully controlling the transmembrane pressure and exploiting the Laplace pressure barriers that arise at the boundary between wetting and non-wetting regions of the membrane, the device suppresses unwanted crossover of the continuous phases. In essence, the capillary pressure required to force a non-wetting liquid through a pore region acts as a self-regulating valve, keeping each phase confined to its designated pathway without the need for external actuation or switching.

The team’s experimental characterization, documented across six main figures and an extensive supplementary package of more than sixty figures and sixteen tables, probed the interfacial restructuring and retained fluid states on the membrane during operation. Contact angle measurements captured in real-time video show directed water transport along the heterogeneous wetting interface, driven by surface energy gradients. Dynamic observations of the oil-water interface on both hydrophilic and hydrophobic membrane regions under varying transmembrane pressure reveal how the fluid states are maintained and how the phase-selective droplet transfer is controlled by the interplay of membrane wettability and channel geometry.

Perhaps the most subtle finding of the study concerns the dual role of shear stress. Shear is essential for demulsification, breaking droplets apart so their phases can be separated. But excessive shear at the membrane surface risks re-emulsification, tearing newly coalesced phases back into fine droplets and undoing the separation. The researchers mapped this trade-off in detail, identifying the operating window in which the gradient contraction channel delivers enough shear to destabilize droplets while the membrane interface experiences conditions that favor coalescence and phase transport rather than droplet re-formation. This balance, they show, is what sustains the device’s remarkable efficiency over extended operation.

The practical implications are considerable. Anti-fouling performance and long-term stability, the two metrics that most often doom membrane technologies in real wastewater service, were both notably enhanced in the new system. Because the opposing emulsion streams are demulsified before contact with the membrane and routed along chemically matched pathways, foulants are less likely to accumulate and clog the pores. The authors also report a techno-economic assessment supported by collaborators at Ocean University of China, suggesting the team has begun to evaluate not just laboratory performance but the commercial viability of the approach. For industries ranging from petroleum refining to food processing and textile manufacturing, where both emulsion types arise in the same facility and are currently handled by separate, sequential treatment trains, a single device that purifies both streams continuously could simplify plant design and reduce operating costs.

The work also builds on, and departs from, a rich lineage of bioinspired separation research. Prior advances include superwetting nanofiber membranes, CO2-responsive switchable membranes, Janus membranes with asymmetric affinities, liquid-infused aerogel systems capable of on-demand emulsification and demulsification, and a Janus channel of membranes reported in Science in 2024 that achieved concurrent oil and water recovery from emulsions. What distinguishes the new study is its explicit targeting of opposing emulsions within a single synchronous process, achieved not by switching a membrane’s properties over time but by distributing different wetting behaviors across space and letting the channel geometry do the rest. The result, the authors write, establishes a new paradigm for synchronous separation and parallel processing of opposite emulsions, paving the way for efficient integrated oil-water separation technology.

Challenges remain before the system can be scaled from laboratory modules to industrial service. Membrane fabrication must be reproducible at large areas, the patterned wettability must withstand years of exposure to surfactants, solvents and temperature swings, and the pressure operating window must tolerate the variability of real waste streams. Yet the fundamental demonstration is striking: a membrane that treats wettability not as a fixed property to be chosen but as a design variable to be patterned, working in concert with fluid mechanics rather than against it. If the reported efficiencies and stability hold up at scale, the humble membrane may finally be ready to handle the full, messy spectrum of emulsified oily waste in one continuous pass.

Subject of Research: A patterned heterowettability membrane with a gradient contraction channel for synchronous, parallel separation of opposing oil-in-water and water-in-oil emulsions.

Article Title: Synchronous and parallel separation of opposing emulsions enabled by a heterowettability membrane

Article References: Zhang, W., Zhang, D., Guan, Y., Li, Y., Geng, S., Li, B., Chen, D., Wang, J., Bao, M., & Wang, Z. (2026). Synchronous and parallel separation of opposing emulsions enabled by a heterowettability membrane. Nature Water. https://doi.org/10.1038/s44221-026-00703-z

Image Credits: AI Generated

DOI: 10.1038/s44221-026-00703-z

Keywords: heterowettability membrane, emulsion separation, oil-water separation, demulsification, shear-induced demulsification, water-in-oil emulsion, oil-in-water emulsion, membrane technology, anti-fouling, Laplace pressure, directional liquid transport, water purification