Fluorine-free nanostructured silica shell creates durable waterproof fabrics

Mar 21, 2026

A one-step technique covalently bonds a nanostructured silica shell onto individual fibers, creating durable superhydrophobic fabrics without nanoparticles or PFAS.

(Nanowerk News) Researchers have developed a one-step technique that covalently bonds a fluorine-free, nanostructured silica shell onto individual textile fibers, producing superhydrophobic fabrics that survive tens of thousands of abrasion cycles and extreme temperatures. The method, called MARS (Molecularly Assembled Robust Superhydrophobic Shell), eliminates the need for discrete nanoparticles or fluorinated chemicals and works on a wide range of natural and synthetic fibers. Published in Nature Communications (“One-step fabrication of superhydrophobic fabrics with stable mechanical performance in harsh conditions”), the work was led by Prof. Dong Zhichao at the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences.

Key Findings

Conventional superhydrophobic treatments for textiles rely on either nanoparticle coatings or finishes based on per- and polyfluoroalkyl substances (PFAS). Nanoparticle layers tend to detach under mechanical stress, clogging fabric pores and reducing breathability. PFAS-based finishes face tightening regulatory restrictions in multiple countries due to their environmental persistence and potential health risks, with fluorochemical bans taking effect from 2026 onward. The MARS technique draws inspiration from springtails, tiny soil-dwelling arthropods whose skin features mushroom-shaped microstructures and nanoscopic ridges that naturally repel water without fluorinated chemistry. To translate this design to textile fibers, the team passes twisted yarns through a petroleum ether solution containing two silane precursors: tetrachlorosilane (TCS) and octadecyltrichlorosilane (OTS). When the coated yarn exits the bath and meets humid air, the solvent evaporates within seconds, and the silanes react to form a nanostructured silica shell bonded directly to the fiber surface. Schematic illustration of the MARS technique. (Image: DONG’s Group) (click on image to enlarge) According to Prof. Dong’s team, the reaction proceeds in two stages. TCS reacts first with hydroxyl groups on natural fibers such as cotton and linen, forming a silica skeleton covalently grafted to each fiber. OTS then anchors long alkyl chains onto the freshly formed silica surface, lowering the surface energy in a manner analogous to the waxy layers found on plant leaves. On synthetic fibers that lack hydroxyl groups, such as polyester and nylon, TCS penetrates slightly into the fiber surface and crosslinks in situ, ensuring broad material compatibility. The resulting nanostructure features mushroom-like silica aggregates measuring 130–170 nm in diameter and tightly adhered silica shells with 20–50 nm feature sizes, creating a hierarchical surface texture. The estimated cost of treating one square meter of cotton fabric is approximately $0.27, dropping to about $0.12 if 75% of the solvent is recovered. Both silane precursors are industrially available commodity chemicals, and TCS can be recycled from silicone waste, supporting the economic feasibility of large-scale manufacturing. A critical advantage of the MARS method is that it operates at the individual fiber level rather than on finished fabric. Treated yarns can be woven, knitted, or embroidered into textiles after coating, and the water-repellent performance survives the mechanical stresses of textile manufacturing. Woven fabrics exhibited water contact angles of 154.7°, knitted fabrics reached 156.1°, and embroidered motifs maintained approximately 161.5°. Even at the single-fiber scale, 20-picoliter droplets showed an apparent contact angle of 160° on individual cotton fibers. Wool, polyester, and nylon fibers all exceeded 156°. Environmental scanning electron microscopy revealed that condensing microdroplets smaller than 2 µm rolled off single fibers once they reached that size, demonstrating water repellency even under cool, saturated conditions. The researchers subjected treated fabrics to durability tests far exceeding what most previous superhydrophobic treatments have undergone. In the Martindale abrasion test, canvas fabric endured 80,000 cycles at 9 kPa pressure while maintaining a contact angle above 150° with less than 5° variation. In the more aggressive Taber test with a 250 g load, treated fabrics survived 20,000 cycles and still measured approximately 156.7°. SEM imaging confirmed that the nanostructured shell remained intact on fiber surfaces after this prolonged wear. In falling sand tests, treated samples withstood 100 cycles of impacts from a cumulative 320 kg of quartz sand while retaining their water-repellent properties. The nanostructured silica shells showed 46.2% less abrasion depth compared to conventional nanoparticle-based coatings, according to the study. Real-world wear simulations reinforced the laboratory results. A treated T-shirt worn during a one-hour treadmill run with a backpack showed no loss of water repellency. In a targeted friction test mimicking shoulder-strap rubbing at 2 Hz, the coating survived more than 600,000 cycles without significant degradation. Knitted fabric retained superhydrophobic properties after 20,000 stretch cycles, and shoe uppers endured 8,000 brushing strokes with negligible change in contact angle. Treated socks worn during 15,000 treadmill steps at approximately 51.3 kPa pressure per step showed only a 1.7° contact angle decrease, while conventionally treated socks lost their water repellency visibly. After 500 cycles of tape peeling at 90°, the contact angle remained around 155°. The MARS coating also proved effective against thermal extremes. Hot water droplets at 85°C bounced cleanly off the fabric. Pressurized hot coffee steam at 100°C and 9 bar did not wet the treated textile. After sequential exposure to boiling water (95°C), liquid nitrogen (-196°C), and boiling water again, the fabric still shed water droplets. Following exposure to 160°C steam from a clothes iron, treated fabrics immediately repelled water, while PFAS-treated control samples became wetted. Low-field NMR measurements showed that steam-exposed treated fabrics retained only weak semi-free water signals, confirming that the covalent silica network blocks vapor condensation more effectively than fluorinated alternatives. The treatment preserved the fabric’s inherent properties. Quantitative fabric hand measurements showed virtually no change in tactile quality: bending rigidity measured 31.7 gf·mm/rad versus 31.1 for untreated controls, and surface roughness was approximately 7.6 µm versus 7.4 µm. Color shifts stayed below 1.0 in the ΔE* metric, meaning the thin silica shells preserved the original appearance. The mass increase from the coating was modest at about 6.1%. The treated fabric also trapped a stable air layer at the textile-water interface, enabling a roughly 40% reduction in hydrodynamic drag at 0.5 m/s flow velocity compared to untreated fabric. Air permeability tests confirmed that breathability was maintained for at least 13.5 hours of continuous submersion. In year-long outdoor exposure spanning temperatures from -16.8°C to 41.2°C and humidity from 9% to 100%, treated fabric maintained superhydrophobicity through all four seasons. A treated T-shirt showed approximately 15% color fading after one year, compared to roughly 45% for an untreated control. Even after extended abrasion and washing, sliding angles remained below 5°. Safety testing showed no concerns with the coating materials. Cytotoxicity assays using NIH 3T3 fibroblasts revealed no significant difference in cell viability between coated fabric and untreated controls over five days. Fabric treated with a PFAS-based repellent, by contrast, exhibited roughly half the viable cell count by day five. The materials in the MARS coating — essentially silica combined with long-chain paraffin wax — are widely considered inert and biocompatible. By addressing the fragility of nanoparticle coatings, the environmental burden of fluorinated finishes, and the loss of fabric comfort that typically accompanies surface treatments, the fiber-level approach demonstrated here could find use across outdoor apparel, protective clothing, medical textiles, and industrial applications. The researchers suggest the method may also extend to emerging fields such as electronic fabrics, display textiles, and wearable health monitors.