The starting point of the study is a familiar frustration in surface science. Superhydrophobic coatings, which repel water so thoroughly that droplets bead up and roll away, typically demand elaborate multi-stage synthesis, energy-hungry processing and, very often, fluorinated compounds that raise environmental and regulatory concerns. Long-chain per- and polyfluoroalkyl substances have come under increasing scrutiny for their persistence, so materials researchers have been searching for fluorine-free routes that do not sacrifice performance. The Chinese team’s answer is to let a single thermal treatment do the chemical heavy lifting, converting a blended precursor into a functional hierarchical surface in one pass through the furnace.

The chemistry behind the transformation is where the elegance lies. UiO-66 is a zirconium-based metal-organic framework, a crystalline lattice of zirconium clusters linked by organic struts, prized for its chemical robustness and thermal stability. When a UiO-66@PDMS composite is calcined, the framework’s organic components burn away and the zirconium nodes are converted into zirconium dioxide, or ZrO2, while the PDMS does not simply vanish. Instead, it partially decomposes, leaving behind oligomeric silicone fragments. The result is a composite microstructure in which inorganic ZrO2 particles derived from the framework are married to residual PDMS-derived oligomers, and it is precisely this combination that endows the coating with its slippery superhydrophobic character.

That dual character matters because superhydrophobicity and slipperiness address different aspects of how water interacts with a surface. A water contact angle exceeding 150 degrees signals that droplets sit atop trapped air pockets with minimal solid contact, so they bead and roll. Slipperiness adds a dynamic dimension: droplets that do make contact slide off easily rather than pinning to the texture. Surfaces that combine both traits resist the accumulation of condensed moisture far better than conventional superhydrophobic materials, which can fail when water vapor infiltrates the texture and condenses inside it, flooding the air pockets and collapsing the water-repellent effect. The USS coating’s composite structure appears to sidestep that failure mode.

The anti-condensation performance is one of the study’s headline results. In humid environments, the coating effectively inhibits water vapor from condensing on treated surfaces, and under low-temperature conditions it extends the freezing-thawing cycle time of water droplets while maintaining stable superhydrophobic properties. That combination is directly relevant to real infrastructure. Condensation on cooled surfaces plagues power transmission equipment, optical lenses, refrigeration systems and building envelopes, and ice formation on aircraft wings, wind turbine blades and power lines remains a costly and hazardous problem. A coating that delays both condensation and freezing, without fluorine, could find wide application in cold and humid climates.

The second major demonstration involves oil-water separation, a technology with urgent environmental stakes given the frequency of oil spills and the volume of oily industrial wastewater. The researchers applied the USS coating to stainless-steel mesh, turning it into a superhydrophobic, oleophilic filter that lets oil pass while blocking water. The numbers are striking: the modified mesh achieved a separation flux of up to 40,000 liters per hour per square meter for trichloromethane, a dense chlorinated solvent that passes through under gravity alone. Flux at that scale means large volumes of oil-water mixture can be processed quickly, which is essential for any practical spill-response or wastewater-treatment deployment.

Equally important is durability, the Achilles heel of many laboratory superhydrophobic surfaces that lose their magic after a few uses. The coated mesh retained a separation efficiency above 90 percent and a water contact angle still exceeding 150 degrees even after 15 separation cycles. Sustained performance across repeated use suggests that the calcined composite structure is mechanically and chemically robust enough to survive continuous contact with liquids, a prerequisite for commercial membranes and filters. The result also aligns with a broader trend in the field, where metal-organic frameworks and their derivatives are increasingly being harnessed as building blocks for superwettable separation materials.

The third function, flame retardancy, is perhaps the most unexpected for a coating that also repels water. When USS-coated cotton fabric was exposed to flame, the coating absorbed flame heat and generated a dense char layer, a carbonaceous barrier that inhibits combustion by shielding the underlying fibers from heat and oxygen. The coating also cut down black smoke emission, addressing a major hazard in textile fires, since smoke inhalation is a leading cause of fire fatalities. Critically, the treated fabric kept its structural integrity and its superhydrophobicity intact through the process, meaning the water repellency does not have to be sacrificed to gain fire protection.

Multifunctionality of this kind is increasingly the benchmark for advanced coatings, because real-world surfaces rarely face a single threat. A tent fabric, a worker’s protective garment or an industrial filter might simultaneously encounter rain, oil contamination and fire risk. Previous efforts have combined such properties by stacking multiple layers or blending numerous additives, often at the cost of complexity and performance trade-offs. The UiO-66@PDMS route achieves the combination from a single precursor and a single thermal step, which simplifies manufacturing and reduces the energy footprint compared with conventional multi-step superhydrophobic coating preparation.

The work, conducted at the College of Materials Science and Engineering at South China University of Technology and supported by the Key-Area Research and Development Program of Guangdong Province and the Natural Science Foundation of Guangdong Province, offers a template that other laboratories can adapt. Because UiO-66 is one of the most studied and chemically tunable metal-organic frameworks, and PDMS is cheap, widely available and easy to process, the strategy could in principle be extended to other substrates and other framework chemistries. For now, the study stands as a demonstration that a furnace, a framework and a silicone can together produce a surface that repels water, resists ice, filters oil and fights fire, all without a single fluorine atom.

Subject of Research: Fluorine-free ultra-slippery superhydrophobic multifunctional coatings fabricated by one-step calcination of UiO-66@polydimethylsiloxane

Article Title: Fabricating ultra-slippery superhydrophobic multifunctional coatings by one-step calcination of UiO-66@polydimethylsiloxane

Article References: Lai, D., Wang, H., Kong, G., Che, C., & Miao, X. (2026). Fabricating ultra-slippery superhydrophobic multifunctional coatings by one-step calcination of UiO-66@polydimethylsiloxane. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13895-2

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13895-2

Keywords: superhydrophobic coating, UiO-66, metal-organic framework, polydimethylsiloxane, calcination, oil-water separation, flame retardancy, anti-condensation, anti-icing, ZrO2, fluorine-free, surface wettability

The secret of superhydrophobicity lies in a partnership between chemistry and geometry. A surface made of low-surface-energy material, such as a silicone or fluorinated compound, naturally resists wetting. But chemistry alone cannot push a flat surface past the superhydrophobic threshold. Roughness is the second ingredient, and it must exist on multiple length scales, with microstructures decorated by even smaller nanostructures. When water meets such a hierarchically rough, low-energy surface, it cannot penetrate the valleys between the peaks. Instead it rests on the tips, with air trapped underneath, a configuration known as the Cassie-Baxter state. The alternative, in which water fully saturates the roughness, is the Wenzel state, and the difference between the two is everything. A droplet in the Cassie-Baxter state rolls off easily; a droplet in the Wenzel state can become pinned so firmly that it behaves more like glue than liquid.

What makes foams special, the authors argue, is that the roughness is not confined to a skin. An open-cell foam is a continuous skeleton of polymer struts surrounding a labyrinth of connected pores, giving the material an enormous internal surface area relative to its weight. That architecture delivers properties a flat film never could: mechanical toughness, compressibility, rapid uptake of liquids into the pore network, and the ability to be squeezed dry and reused again and again. The physics of that uptake is governed by capillary action, described classically by the Lucas-Washburn equation, which relates how fast a wetting liquid penetrates a pore to the pore radius and the liquid’s surface tension. The review emphasizes that connected pores, capillary-driven infiltration and even deliberate wettability gradients inside the foam determine how efficiently oil can be absorbed, a point of direct consequence for the field’s flagship application.

That application is oil spill cleanup. When a foam is both superhydrophobic and superoleophilic, it drinks oil and refuses water, making it a selective sponge for petroleum slicks. Polyurethane foam, cheap, elastic and commercially ubiquitous, has been the workhorse substrate. Researchers have modified it with silica nanoparticles, polysiloxane-modified clay nanotubes, zinc oxide microrods wrapped in carbon cloth, silanized nanoclay and magnetite particles that let a magnetic field steer the saturated sponge. More recent work has added photothermal coatings, layers that convert sunlight into heat, so that viscous crude oil, which barely flows at ambient temperature, warms up and wicks into the foam faster. One 2025 study described a fire-extinguishing polyurethane foam for solar-assisted recovery of viscous crude oil, combining absorption with an intrinsic safety feature.

Polyurethane is only the beginning of the materials list the review assembles. Polystyrene foams, including those made by high internal phase emulsion templating, a technique that produces well-defined, highly connected pore structures, have been engineered with carbon black or graphene for photothermal oil capture and continuous separation of even emulsified oil-water mixtures. Polypropylene and polyethylene foams, often fabricated by supercritical carbon dioxide foaming, a solventless process in which pressurized gas expands the polymer into a microcellular structure, have shown robust superhydrophobicity, self-cleaning behavior, anti-icing performance and selective oil absorption. Ethylene propylene diene monomer rubber, polyethylene terephthalate and even biodegradable polylactic acid have all been converted into water-repellent sponges, the latter sometimes by a simple skin-peeling method that exposes a naturally rough interior.

A quieter revolution in the field concerns where the chemistry comes from. Fluoroalkyl silanes and other fluorinated modifiers are superb at lowering surface energy, but their toxicity and environmental persistence are increasingly unacceptable. The review highlights a shift toward fluorine-free systems: silicone-based chemistries, hydrophobic silica, stearic acid, and, strikingly, lignin, the aromatic polymer that woody plants use to waterproof their own cell walls. Lignin-based polyurethane foams, lignin nanosphere coatings and biomass-derived porous carbon combined with carbon nanotubes in melamine foam all demonstrate that nature’s own hydrophobic building blocks can do the job. Bioinspired design runs through the whole field, from lotus-leaf mimicry to a 2025 foam modeled on dragonfly wings, and even to self-healing surfaces that repair mechanical damage the way living tissue does.

The applications extend well beyond mopping up oil. Because water cannot adhere to these surfaces, they resist icing, and superhydrophobic polyethylene and polyurethane foams have been demonstrated for anti-icing and photothermal deicing, melting frost off their own surfaces using embedded light-absorbing fillers such as graphene or carbon nanotubes. The trapped air and low density of polymer foams make them excellent thermal insulators, and some formulations add flame retardants, producing foams that repel water and resist fire simultaneously, in one case with a built-in fire alarm response. Conductive fillers such as carbon nanotubes, MXene nanosheets and graphene turn the foams into pressure sensors and electromagnetic interference shields, so the same sponge that cleans an oil slick might also monitor compression or block radio-frequency noise in damp environments.

Yet the review is candid about why these materials are not already everywhere. Coatings of nanoparticles bonded weakly to a foam surface wear away under abrasion, and once the delicate micro-nano texture is destroyed, the Cassie-Baxter state collapses and the foam wets permanently. Fluorinated chemistry raises regulatory and toxicological concerns. Most laboratory syntheses involve dip-coating, chemical vapor deposition, sol-gel processing, electrospinning or freeze-drying, none of which scale gracefully or cheaply to industrial volumes, and the authors point to persistent discrepancies between laboratory results and real-world performance. Durability, scalability and cost form a triangle of constraints that the field has not yet fully escaped, a theme echoed in broader assessments of superhydrophobic surface commercialization.

The path forward, the authors suggest, lies in fluorine-free chemistries, self-repairing structures borrowed from biology, and fabrication processes that are scalable at reasonable cost. Some of those pieces already exist in prototype form: mechanochemically durable self-healing coatings, water-based nonfluorinated dispersions for large-area application, extrusion plus supercritical foaming routes that use commodity processing equipment, and even three-dimensional printable self-foaming silicone inks that produce bulk superhydrophobic objects rather than fragile surfaces. If durability and manufacturing can be solved together, superhydrophobic foams could move from demonstration papers to deployed products, cleaning spills, shedding ice, insulating buildings and sensing pressure, all while refusing, like the lotus leaf, to let water stick.

Subject of Research: Superhydrophobic polymeric foams: wetting theory, fabrication methods and applications in oil-water separation and multifunctional materials

Article Title: Superhydrophobic polymeric foam: A review

Article References: Patel, P., Pichare, P., & More, A. P. (2026). Superhydrophobic polymeric foam: A review. Polymer Bulletin, 83(12), Article 663. https://doi.org/10.1007/s00289-026-06713-x

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06713-x

Keywords: superhydrophobic foams, Cassie-Baxter state, Wenzel state, oil spill cleanup, polyurethane foam, supercritical CO2 foaming, lignin, fluorine-free coatings, photothermal conversion, anti-icing, electromagnetic shielding, self-healing surfaces

The research centers on microencapsulated phase change materials, or mPCMs, tiny core-shell particles in which a substance that melts and freezes at a useful temperature is locked inside a polymer wall. Phase change materials absorb large amounts of latent heat as they melt and release that heat as they solidify, acting as thermal batteries that buffer temperature swings. The catch is that the most common PCMs are solid-liquid paraffins that leak when they melt, which is why encapsulation is essential. Microencapsulation solves the leakage problem, dramatically increases the surface area available for heat transfer, and allows the particles to be blended directly into concrete, coatings, textiles, or packaging without any special handling.

What makes the Turkish team’s work novel is the shell material. Most commercial and laboratory mPCMs rely on formaldehyde-based resins such as melamine-formaldehyde or urea-formaldehyde, which can release harmful substances during synthesis and use, or on polystyrene and PMMA, which are flammable. The researchers instead dissolved waste PVC, sourced from a commercial leather company, together with 1-tetradecane, a paraffin that melts at around 5 degrees Celsius, in tetrahydrofuran and used a solvent evaporation technique to precipitate PVC shells around droplets of the paraffin. It is the first time waste PVC has been used this way for a low-temperature, cold-storage PCM, and the choice is doubly clever because PVC is inherently flame retardant, with a limiting oxygen index between 40 and 45, far above the threshold of 26 that separates flame-retardant polymers from ordinary combustible ones.

The synthesis itself is a piece of practical process chemistry. Solution A contained 26 grams of sodium chloride and 9 grams of gelatin dissolved in deionized water, with the salt raising the ionic strength to keep the water from dissolving the THF and the gelatin acting as a natural, biodegradable surfactant that stabilizes the emulsion. Solution B held the waste PVC powder and 1-tetradecane in THF. When B was dripped into the vigorously stirred A, droplets formed whose size depended on how they were added: a Pasteur pipette produced large particles, a micropipette produced small ones. The emulsion was then heated to 56 degrees Celsius so the THF evaporated, leaving behind hardened capsules that were filtered, washed with water and ethanol, and dried. Remarkably, the final particle diameter tracked the initial droplet size, giving the team a simple dial for tuning capsule dimensions, something conventional in-situ polymerization cannot easily achieve.

Two particle populations emerged. The small-particle capsules, designated mPCM/SP, averaged 145 micrometers, while the large-particle capsules, mPCM/LP, averaged 612 micrometers. Both were unimodally distributed, a sign of a well-controlled process. Fourier transform infrared spectroscopy confirmed that the characteristic C-Cl stretching peak of PVC at 1750 per centimeter persisted in the capsules and that the CH2 stretching bands of the paraffin core remained intact, indicating that core and shell coexist without strong chemical interaction, exactly what a good encapsulation should deliver. Differential scanning calorimetry showed that the capsules behave isothermally like the pure paraffin, with melting temperatures of 5.0 and 4.7 degrees Celsius and latent heats of 126.7 and 136.9 joules per gram for the large and small particles respectively. Encapsulation ratios reached 66.5 percent for the large particles and 71.9 percent for the small ones, squarely within the 60 to 90 percent range typical of the best polymer-shelled paraffin microcapsules in the literature.

One subtlety the authors confront head-on is supercooling. The encapsulated paraffin froze at slightly lower temperatures than the bulk material, a well-documented consequence of the shell adding thermal resistance and constraining nucleation within the confined core. Crucially, however, the capsules still solidified above 1 degree Celsius, comfortably inside the operating window for cold-chain and anti-icing service, and the shift is partly an artifact of the relatively fast 5 degrees per minute DSC scanning rate, which is known to exaggerate apparent supercooling. Repeated cycling showed deviations of less than 1 degree Celsius in transition temperatures and about 1.2 percent in latent heat, confirming that the phase change process remains fully reversible and that encapsulation has not degraded the PCM’s intrinsic properties.

Durability testing was equally convincing. The capsules endured 1,000 accelerated thermal cycles between -20 and 30 degrees Celsius, the equivalent of roughly 15 years of daily freeze-thaw service, with DSC signals reproduced almost perfectly after every 100 cycles and FT-IR spectra after 1,000 cycles showing no chemical change. Leak tests were brutal in their simplicity: samples were frozen at -18 degrees Celsius for 12 hours, then baked at 50 degrees Celsius for another 12 hours on filter paper. No visible PCM leakage appeared, and weight losses were a negligible 0.05 to 0.08 percent. Thermogravimetric analysis showed the capsules degrade at higher temperatures than the free paraffin, meaning the PVC shell genuinely protects the core.

The flame retardancy results may be the study’s most distinctive contribution. Because standard limiting oxygen index tests require rectangular samples that microparticles cannot form, the team built a calibration curve by burning reference plastics of known LOI, including expanded polystyrene, polyacrylonitrile, PET, nylon 66, and ABS, and correlating burning times with literature values. Using the resulting equation, they estimated LOI values of 27.6 percent for mPCM/SP and 28 percent for mPCM/LP, above the flame-retardancy threshold and a dramatic improvement over pure 1-tetradecane, whose LOI of 17 means it burns in ordinary air. The mechanism is intrinsic: when PVC decomposes it releases hydrogen chloride gas, which suppresses combustion and promotes a protective char layer. Unlike conventional flame-retardant PCM systems that rely on added ammonium polyphosphate or expandable graphite, this fire resistance comes free with the recycled shell material itself.

The application vision spans two very different worlds. In the sub-5-degree melting range, the capsules are natural candidates for cold-chain packaging, refrigerated transport containers, and insulated panels, where they would absorb heat whenever temperatures rise and release it back as things cool, smoothing out the fluctuations that spoil food and vaccines. In civil infrastructure, mixed into concrete pavements, bitumen binders, or surface coatings, the latent heat released as the capsules freeze could slow the drop of road surface temperature, delay ice nucleation, and reduce ice adhesion, potentially cutting dependence on corrosive chloride deicers. Earlier work by Farnam and colleagues demonstrated the pavement concept with other PCMs, and the Turkish team’s flame-retardant, waste-derived capsules would bring an added safety margin to exactly that use case.

Beyond the immediate applications, the study is a template for what materials scientists call waste valorization: converting an environmental liability into a high-value functional material. PVC is notoriously difficult to recycle through conventional plastic streams because its chlorine content and rheology make it incompatible with aliphatic polyesters and polyolefins, so it is usually landfilled or incinerated. Here, that same chlorine chemistry becomes an asset, delivering flame retardancy that other shell polymers must buy with additives. The process also avoids the nastier solvents common in encapsulation chemistry, using halogen-free THF whose high vapor pressure makes recovery straightforward. As the authors conclude, the work validates a route from a persistent waste problem to thermally reliable, fire-safe, size-tunable microcapsules, and it broadens the reach of phase change material technology into the low-temperature regime where cold chains, winter roads, and a warming world’s cold-storage demands increasingly intersect.

Subject of Research: Flame-retardant microencapsulated phase change materials synthesized from waste poly(vinyl chloride) for low-temperature thermal energy storage and anti-icing applications

Article Title: Novel flame retardant microencapsulated phase change materials from waste poly(vinyl chloride) for maintaining cold and anti-icing applications

Article References: Alkan, C., & Alakara, E. H. (2026). Novel flame retardant microencapsulated phase change materials from waste poly(vinyl chloride) for maintaining cold and anti-icing applications. Journal of Materials Science: Polymers, 1(1), Article 16. https://doi.org/10.1007/s44493-026-00017-2

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00017-2

Keywords: phase change materials, waste PVC recycling, microencapsulation, thermal energy storage, flame retardancy, 1-tetradecane, anti-icing, cold chain, latent heat, solvent evaporation, supercooling, sustainable materials