Anti-wetting Properties Research Articles

Characterization of membrane wetting phenomenon by ionic liquid via ultrasonic time-domain reflectometry (UTDR)

Ionic liquids (ILs) are becoming attractive solvents or catalysts in many industries, thus energy-efficient membrane-based technologies for the purification and concentration of ILs are gaining attention. Membrane wetting by ILs is recognised as the major challenge in membrane processes, but limited information is available. In this study, the dynamics of wetting of commercial hydrophobic polytetrafluoroethylene (PTFE) membranes by a water-immiscible IL, trihexyl(tetradecyl)phosphonium (THTDP), was characterized by an online and non-destructive technique – ultrasonic time-domain reflectometry (UTDR). In the UTDR analysis, information such as resistance of membrane to IL penetration, duration and rate of wetting process can be deduced from the changes in arrival time and amplitude of reflected peak from the IL/pore-air interface, i.e., pores in pristine hydrophobic membrane are completely-filled with air until IL penetration that displaces the pore-air. The UTDR analysis was further supported by offline and destructive methods typically used to characterize membrane such as Fourier-transform infrared spectroscopy (FTIR), contact angle (CA), liquid entry pressure (LEP) and field emission scanning electron microscopy (FESEM). Through the abovementioned analyses, it was concluded that the commercial hydrophobic PTFE membranes exhibited poor anti-wetting properties against concentrated THTDP IL due to chemical affinity between IL and membrane.

Antibacterial fabric with contradictory functions of water repellency and absorbency realized by electrophoretic deposition of hydrophobic SiO2 and hydrophilic ZnO nanoparticles

Clothing and fabrics used in household and industrial applications can cause human-to-human cross-infection by residual bacteria attached to their surfaces. In particular, for fabrics used in the medical and healthcare sectors, it is vital to use highly antibacterial fabrics to prevent secondary infections caused by body fluids. In this work, antibacterial fabrics with strong water repellency were developed by electrophoretic deposition (EPD) of zinc oxide (ZnO) and hydrophobic silicon dioxide (SiO2) nanoparticles. The top layer of hydrophobic SiO2 nanoparticles prevents direct adhesion of bacterial droplets, while the bottom layer of hydrophilic ZnO nanoparticles provides antibacterial properties against the residual bacteria on the fabric. As a result, the developed fabrics can simultaneously reduce droplet adhesion and bacteria viability, effectively lowering the risk of bacterial infection. The ability to express these opposing wettabilities can be achieved by our EPD process, which can deposit various nanoparticles in porous form using electric fields on a non-conductive substrate. We expect that the fabrics developed in this work can be applied to various fields that require both antibacterial and antiwetting properties.

Proven Anti-Wetting Properties of Molybdenum Tested for High-Temperature Corrosion-Resistance with Potential Application in the Aluminum Industry.

The behavior of Mo in contact with molten Al was modelled by classical molecular dynamics (CMD) simulation of a pure Mo solid in contact with molten Al at 1200 K using the Materials Studio®. Results showed that no reaction or cross diffusion of atoms occurs at the Mo(s)–Al(l) interface, and that molten Al atoms exhibit an epitaxial alignment with the exposed solid Mo crystal morphology. Furthermore, the two phases {Mo(s) and Al(l)} are predicted to interact with weak van der Waals forces and give interfacial energy of about 203 mJ/m2. Surface energy measurements by the sessile drop experiment using the van Oss–Chaudhury–Good (VCG) theory established a Mo(s)–Al(l) interface energy equivalent to 54 mJ/m2, which supports the weak van der Waals interaction. The corrosion resistance of a high purity (99.97%) Mo block was then tested in a molten alloy of 5% Mg mixed in Al (Al-5 wt.%Mg) at 1123 K for 96 h, using the ALCAN’s standard “immersion” test, and the results are presented. No Mo was found to be dissolved in the molten Al-Mg alloy. However, a 20% mass loss in the Mo block was due to intergranular corrosion scissoring the Mo block in the ALCAN test, but not as a result of the reaction of pure Mo with the molten Al-Mg alloy. It was observed that the Al-Mg alloy did not stick to the Mo block.

Superhydrophobic modification of electrospun nanofibrous Si@PVDF membranes for desalination application in vacuum membrane distillation

Superhydrophobic nanofibers have received prominent attention owing to their exceptional properties and researchers are focused on developing high-performing MD membranes. Herein, we fabricate superhydrophobic electrospun nanofibrous membranes using polyvinylidene fluoride (PVDF) solutions with silica nanoparticles (0 wt% to 6 wt%) to create multiscale (or hierarchical) surface roughness. For superhydrophobicity, the composite membranes (Si@PVDF) were subjected to a two-step modification that included acid pre-treatment and silanization with fluoroalkylsilane (FAS) compound of low surface energy. The acid pre-treatment enhances the hydroxyl group of SiO2 nanoparticles and create active sites in abundance for silanization. The modified membranes (FAS-Si@PVDF-A) having 6 wt% SiO2 showed excellent wetting resistance with water contact angle (WCA) up to 154.6 ± 2.2°, smaller average pore size of 0.27 ± 0.3 μm, and high liquid entry pressure (LEP) of 143 ± 4 kPa. It was observed, increasing silica content decreased the fiber diameter and average pore size and increased WCA and LEP of modified membranes. The modified superhydrophobic membranes gave stable permeate flux, exhibited strong wetting resistance and excellent salt rejection in vacuum membrane distillation (VMD) test. The optimal FAS-Si@PVDF-A membrane (6 wt% SiO2) of thickness 98 ± 5 μm produced a stable permeate flux of more than 11.5 kg m−2 h−1 and salt rejection as high as 99.9% after 22 h of continuous operation using NaCl solution (3.5 wt%) as feed. Therefore, this modification provided superhydrophobic membranes possessing robust anti-wetting properties with significant permeability and has encouraging application in membrane distillation for desalination.

Nanofiltration-Inspired Janus Membranes with Simultaneous Wetting and Fouling Resistance for Membrane Distillation.

Membranes with robust antiwetting and antifouling properties are highly desirable for membrane distillation (MD) of wastewater. Herein, we have proposed and demonstrated a highly effective method to mitigate wetting and fouling by designing nanofiltration (NF)-inspired Janus membranes for MD applications. The NF-inspired Janus membrane (referred to as PVDF-P-CQD) consists of a hydrophobic polyvinylidene fluoride (PVDF) membrane and a thin polydopamine/polyethylenimine (PDA/PEI) layer grafted by sodium-functionalized carbon quantum dots (Na+-CQDs) to improve its hydrophilicity. The vapor flux data have confirmed that the hydrophilic layer does not add extra resistance to water vapor transport. The PVDF-P-CQD membrane exhibits excellent resistance toward both surfactant-induced wetting and oil-induced fouling in direct contact MD (DCMD) experiments. The impressive performance arises from the fact that the nanoscale pore sizes of the PDA/PEI layer would reject surfactant molecules by size exclusion and lower the propensity of surfactant-induced wetting, while the high surface hydrophilicity resulted from Na+-CQDs would induce a robust hydration layer to prevent oil from attachment. Therefore, this study may provide useful insights and strategies to design novel membranes for next-generation MD desalination with minimal wetting and fouling propensity.

Preparation and vacuum membrane distillation performance of a superhydrophobic polypropylene hollow fiber membrane modified via ATRP

Superhydrophobic polypropylene hollow fiber membranes were fabricated using single- and multi-step atom transfer radical polymerization methods. The degree of grafting was improved by intermittently adding equal doses of monomers. Membrane morphology and anti-wetting properties of the membranes produced using the two methods were thoroughly investigated to understand the influence of structure on vacuum membrane distillation (VMD) performance. Initial monomer dosages of 20% and 30% facilitated the production of superhydrophobic modified membranes with water contact angles of 167.9° and 179.0°, respectively. The samples with the highest liquid entry pressure were produced using an initial monomer dosage of 20%, and were selected for the VMD experiments. Testing was conducted for 21 h and indicated that the modification method significantly affected VMD performance. This was attributed to the prominent differences in morphology and pore distribution. The average flux of the membrane produced with 20% monomer using the single-step method was 11.01 kg/m2h, which was 4.53 kg/m2h higher than that of the unmodified membrane; the long-term stability was superior. Although the membrane produced using the multi-step method exhibited an excellent average flux of 12.71 kg/m2h, the performance was highly unstable, and flux suddenly dropped after 6 h. Furthermore, the rejection performance was unsatisfactory. Overall, the two new membranes showed pronounced distinctions in VMD performances, which agrees well with our hypotheses.

Innovative hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride (PVDF) composite membrane for vacuum membrane distillation

Though membrane distillation (MD) has gained more and more attention in the field of desalination, the wetting phenomenon was still a non-negligible problem. In this work, a method combined dip-coating and UV in situ polymerization for preparing hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride composite membranes. This composite membrane consisted of a top thin hydrophobic coating layer and hydrophilic substrate membrane. In terms of anti-wetting properties, contact angle and liquid entry pressure of all composite membranes (except for those based on 0.45 μm) exceeded 160° and 0.3 MPa, respectively. In particular, the desalination performance was tested in vacuum membrane distillation tests by feeding 3.5% (mass) saline solution (NaCl) at 60 °C. The composite membranes with larger support pore size and lower PFPE content had higher membrane distillation flux. And for stability tests (testing the 0.22 μm membrane coated by 5% (mass) PFPE), the highest MD flux 29.08 kg·m−2·h−1 and stable salt rejection (over 99.99%) during the period. Except that, the effects of coating material concentration and pore sizes of substrate membrane were also investigated for surface morphology and topography, porosity, mechanical strength and pore size characteristics. This work provided a simple and effective alternative to prepare excellent hydrophobic composite membranes for MD applications.

A water-repellent PVDF-HNT membrane for high and low concentrations of oxytetracycline treatment via DCMD: An experimental investigation

• Synthesis of PVDF membrane using halloysite and montmorillonite was reported. • Anti-wetting properties of PHNT membrane met the MD requirements. • A higher permeability was observed for PHNT membrane. • Separation mechanism of OTC removal by PHNT membrane was proposed. Oxytetracycline (OTC) is classified as contaminants of emerging concern (CEC) and has been detected in significant quantities in aquaculture wastewater in several countries. This study introduces an alternative treatment using a water-repellent poly(vinylidene fluoride)-halloysite (PHNT) membrane via direct contact membrane distillation (DCMD). The membrane was fabricated using halloysite nanotube (HNT) and poly(vinylidene fluoride) (PVDF) was used as a base polymer, which was dissolved in triethyl phosphate (TEP) via immersion precipitation. The performance of HNT as an additive was compared with montmorillonite (MMT). The water repellent properties were evaluated using a porometer, goniometer, and scanning electron microscope to meet the membrane requirements for direct contact membrane distillation (DCMD) and gain insights into the PHNT separation mechanism. The fabricated membrane obtained the desired anti-wetting properties after the addition of HNT in the PVDF matrix, where the contact angle and liquid entry pressure were 137° ± 0.79 and 2.11 ± 0.03 bar, respectively. The OTC removal by the PHNT membrane was experimentally tested for high and low OTC concentrations. The presence of HNT enhanced the permeate flux to 5.69 L/m 2 ·h (100 ppm) and 5.35 L/m 2 ·h (10 ppm) with 97% and 90% of OTC removal, respectively. Complete removal (100%) of 10 ppm OTC solution proved a successful separation of low OTC concentration by the 0.5% PHNT membrane.

Carnauba Wax/Halloysite Nanotube with Improved Anti-Wetting and Permeability of Hydrophobic PVDF Membrane via DCMD.

The hydrophobic membranes have been widely explored to meet the membrane characteristics for the membrane distillation (MD) process. Inorganic metal oxide nanoparticles have been used to improve the membrane hydrophobicity, but limited studies have used nano clay particles. This study introduces halloysite nanotube (HNT) as an alternative material to synthesis a hydrophobic poly(vinylidene fluoride) (PVDF)-HNT membrane. The PVDF membranes were fabricated using functionalized HNTs (e.g., carnauba wax and 1H,1H,2H,2H-perfluorooctyl-trichlorosilane (FOTS)). The results were determined by Fourier transform infrared-attenuated total reflection, scanning electron microscope, goniometer and porometer to determine the desired hydrophobic membrane for direct contact membrane distillation (DCMD). The addition of FOTS-HNT (fs-HNT) and carnauba wax-HNT (fw-HNT) in the PVDF membrane enhanced the water contact angle (CA) to 127° and 137°, respectively. The presence of fw-HNT in the PVDF membrane exhibited higher liquid entry pressure (LEP) (2.64 bar) compared to fs-HNT in the membrane matrix (1.44 bar). The PVDF/fw-HNT membrane (Pfw-HNT) obtained the highest flux of 7.24 L/m2h with 99.9% salt removal. A stable permeability in the Pfw-HNT membrane was obtained throughout 16 h of DCMD. The incorporation of fw-HNT in the PVDF membrane had improved the anti-wetting properties and the membrane performance with the anti-fouling effect.

A Mini Review on Antiwetting Studies in Membrane Distillation for Textile Wastewater Treatment

The textile industry is an important contributor to the growth of the global economy. However, a huge quantity of wastewater is generated as a by-product during textile manufacturing, which hinders the ongoing development of textile industry in terms of environmental sustainability. Membrane distillation (MD), which is driven by thermal-induced vapor pressure difference, is being considered as an emerging economically viable technology to treat the textile wastewater for water reuse. So far, massive efforts have been put into new membrane material developments and modifications of the membrane surface. However, membrane wetting, direct feed solution transport through membrane pores leading to the failure of separation, remains as one of the main challenges for the success and potential commercialization of this separation process as textile wastewater contains membrane wetting inducing surfactants. Herein, this review presents current progress on the MD process for textile wastewater treatment with particular focuses on the fundamentals of membrane wetting, types of membranes applied as well as the fabrication or modification of membranes for anti-wetting properties. This article aims at providing insights in membrane design to enhance the MD separation performance towards commercial application of textile wastewater treatment.

Robust dual-layered omniphobic electrospun membrane with anti-wetting and anti-scaling functionalised for membrane distillation application

A robust dual-layer superhydrophobic and omniphobic electrospun nanofiber membrane was developed for membrane distillation application, especially with feed that contains surfactant and dissolved organic compounds. 1H, 1H, 2H, 2H-Perfluorooctyltriethoxysilane (FAS) functionalising of the electrospun polyvinylidene fluoride-co-hexafluoropropylene (E-PVDF-HFP) membrane, followed by surface grafting with FAS-functionalised zinc oxide (ZnO) nanoparticles, achieved low membrane water sliding angle with re-entrant morphologies on the membrane surface. Field-emission scanning electron microscopy with energy-dispersive X-ray images revealed the regular and uniform formation of re-entrant structures due to the ZnO nanoparticles. The optimised 25% w/w ZnO (ePFP-25Z) membrane achieved the highest contact angles for water (>161°), oil (131.5° ± 1.8°) and ethanol (131° ± 2.9°), had the lowest surface energy (0.75 ± 0.43 mN m−1) and high surface roughness (3.26 μm). The ePFP-25Z membrane maintained a stable membrane distillate flux and salt rejection (>99.9%) even after 80 h operation with 0.1 mM sodium dodecyl sulphate in super-saline solution (1 M NaCl). Anti-scaling and anti-wetting properties were illustrated in the presence of the dissolved organic compounds humic acid and alginate in super-saline feed.

Development of robust and superamphiphobic membranes using reduced graphene oxide (rGO)/PVDF-HFP nanocomposite mats for membrane distillation

One-step tailoring of robust superamphiphobicity on nanocomposite mats with superior antifouling and anti-wetting properties for membrane distillation.

ZnO Nanowires@PVDF nanofiber membrane with superhydrophobicity for enhanced anti-wetting and anti-scaling properties in membrane distillation

The anti-wetting and anti-scaling abilities of membrane are two critical properties for the membrane distillation. In this work, a superhydrophobic hybrid composite nanofiber membrane with the construction of hydrophobic ZnO nanowires on PVDF nanofiber membrane (P–ZnO@PVDF) based on hydrothermal method and chemical vapor deposition (CVD) was presented. Imitating the growth of grass was employed to enhance the adhesion between ZnO nanowires and PVDF nanofiber membrane. The P–ZnO@PVDF membrane exhibited high porosity, narrow pore size distribution, superhydrophobicity, anti-wetting and anti-scaling, owing to the slip and Cassie-Baxter state caused by introduction of hydrophobic ZnO nanowires. Moreover, the membrane with robust durability presented the salt rejection of 99.9% and a stable permeation flux of 15.7 L m−2 h−1 for simulated seawater at the feed temperature of 60 °C and the distillate temperature of 20 °C after 60 h operation. The hybrid composite nanofiber membrane is to be a potential candidate for long-term operation of membrane distillation.

Nafion-PTFE hollow fiber composite membranes for improvement of anti-fouling and anti-wetting properties in vacuum membrane distillation

Nafion-PTFE hollow fiber composite membranes were fabricated and applied in vacuum membrane distillation (VMD) process to improve the anti-fouling and anti-wetting performance in the presence of oil and surfactant. The composite membrane exhibited an underwater super-oilphobic property according to the contact angle test. The VMD performance when treating saline feed containing 3.5 wt% NaCl and 1000 ppm mineral oil for the composite membrane behaved a stable flux for 40 h. In construct, an immediate and sharply-declined flux was observed for the pristine PTFE, indicating the significant improvement in the anti-fouling property. Meanwhile, the composite membrane also alleviated the wetting phenomena caused by the surfactant comparing with the pristine PTFE membrane, and the Nafion-PTFE composite membrane behaves a stable flux and high salt rejection higher than 99.99% for 60 h treating saline feed containing O/W emulsions. The pressure depression effect of the Nafion layer on the mass transfer was analyzed. It was found that the depression could be reduced with the increasing of the feed temperature and the enhancement of the corresponding effective pore diameter of the Nafion layer, that the pressure depression factor decreased from 0.23 to 0.04 with the feed temperature increasing from 60 °C to 75 °C.

In-situ silica nanoparticle assembly technique to develop an omniphobic membrane for durable membrane distillation

This work reported that a novel omniphobic membrane distillation (MD) membrane was successfully fabricated by constructing a re-entrant microstructure via in-situ silica nanoparticle (SiNPs) growth on an electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/3-aminopropyl-triethoxysilane (APTES) nanofibrous membrane, and subsequent hydrophobization. Introducing APTES provided the nucleation sites for in situ SiNPs growth on the hydrophobic nanofibers for re-entrant structure construction. After hydrophobization, the final membrane exhibited outstanding omniphobicity with high contact angle values of 151.49°, 140.64°, 119.59°, and 107.5° to water, mineral oil, 4 mM sodium dodecyl sulfate (SDS) and ethanol, respectively. More importantly, the prepared omniphobic membrane showed satisfactory wetting resistance in a feed solution containing a 3.5 wt% NaCl and 0.4 mM SDS, and the salt rejection was ~100%. In addition, the omniphobic membrane also demonstrated robust scaling resistance, which was in sharp contrast to the PVDF-HFP membrane. Meanwhile, during treating a mineral oil-in-saline (3.5 wt% NaCl) water emulsion, the omniphobic membrane displayed outstanding anti-wetting and anti-fouling properties, indicated by a steady state permeate flux and ~100% stable salt rejection during the continuously 72 h tests. These overall findings indicated that the prepared omniphobic membranes have great potential in MD for challenging industrial wastewaters.

How drain flies manage to almost never get washed away

Drain flies, Psychodidae spp. (Order Diptera, Family Psychodidae), commonly reside in our homes, annoying us in our bathrooms, kitchens, and laundry rooms. They like to stay near drains where they lay their eggs and feed on microorganisms and liquid carbohydrates found in the slime that builds up over time. Though they generally behave very sedately, they react quite quickly when threatened with water. A squirt from the sink induces them to fly away, seemingly unaffected, and flushing the toilet with flies inside does not necessarily whisk them down. We find that drain flies’ remarkable ability to evade such potentially lethal threats does not stem primarily from an evolved behavioral response, but rather from a unique hair covering with a hierarchical roughness. This covering, that has never been previously explored, imparts superhydrophobicity against large droplets and pools and antiwetting properties against micron-sized droplets and condensation. We examine how this hair covering equips them to take advantage of the relevant fluid dynamics and flee water threats in domestic and natural environments including: millimetric-sized droplets, mist, waves, and pools of water. Our findings elucidate drain flies’ astounding ability to cope with a wide range of water threats and almost never get washed down the drain.

Controllably facile design of electrophoretic-induced film-forming of nano tungsten oxide (VI) and their anti-wetting functionalization

There is keen interest for designing promising tungsten oxide (VI, WO3) films or coatings due to their wide applications in fields of energy, engineering, etc. Thus, this paper firstly introduce a novel convenient method of electrophoretic assembly technique (EAT) in an optimal stable suspension of isopropyl alcohol, PEG-1000 and polyethyleneimine for designing the promising anti-wetting functional WO3 (VI) films with relative rough structures and uniform distribution in mild conditions. The product possess a high crystallinity and pureness by x-ray powder diffraction analysis. The EAT dynamic behaviours of WO3 (VI) nanoparticles are investigated in detail. Moreover, obtained films shows excellent anti-wetting properties after suface modification, and the hydrophobic studies results demonstrate that product have a high static water CA of approximate 169° and keep nearly stable even after ultralong exposure time (360 d), and show outstanding properties of anti-soaking, impacting-proof, and moisture resistance even in high relative humidity (90%). These breakthroughs will substantially push forward the convenient processing of other anti-wetting functional coatings with wide potential applications.

Improving Corrosion Resistance of Aluminosilicate Refractories towards Molten Al-Mg Alloy Using Non-Wetting Additives: A Short Review.

The corrosion of refractories in contact with high temperature aluminum-magnesium alloys leads to contamination of the Al-Mg alloy products by solid impurities from degraded refractories. Where both the spinel and corundum phases form in the refractories, cracks are generated and propagated by diffusion of molten Al-Mg, resulting in severe corrosion. In this review paper, the corrosion phenomenon is discussed, and published work is summarized, supplemented by our recent experimental results. Using the Alcan immersion test, materials based on white-fused mullite (WFM) were evaluated for their corrosion resistance and interfacial behavior. WFM was modified using different 2-wt.% of non-wetting additives (NWAs), such as BaSO4, CaF2, Secar®71 cement and wollastonite to improve their performance when in contact with molten Al-Mg alloy at 850 °C for 96 h. The mechanical properties of the samples such as flexural and compressive strength were evaluated, in addition to X-ray diffraction and microscopic analysis (optical and scanning electron microscopy coupled with X-ray elemental mapping). It was observed that cracks formed in samples were promoted with only BaSO4, CaF2, Secar®71 cement or wollastonite. However, cracks did not appear in the sample promoted with both 1-wt.% CaF2 and 1-wt.% BaSO4, because of improved anti-wetting properties in addition to inhibiting spinel (MgAl2O4) formation, which is the main cause of the cracks. This is a significant finding in the prevention of cracks and improvement of the refractory corrosion resistance.

Hierarchical Janus membrane with superior fouling and wetting resistance for efficient water recovery from challenging wastewater via membrane distillation

Conventional hydrophobic membranes are susceptible to membrane fouling and pore wetting, impeding the applications of membrane distillation (MD) processes for water recovery from complex wastewater. To address these challenges, we herein developed a novel Janus membrane by a hybrid plant-derived polyphenols coating and polyelectrolytes layer-by-layer assembly strategy. Through alternative deposition of catechol/chitosan and polyethylenimine (PEI) on top of a hydrophobic polyvinylidene fluoride (PVDF) substrate, a Janus membrane with a superhydrophilic and defect-free top layer was achieved. The synergistic effects of covalent bonding, non-covalent interactions, and electrostatic interactions between neighboring coatings endowed the membrane with robust chemical stability in the pH range of 2–12. In comparison with the pristine PVDF membrane, the Janus membrane exhibited remarkably stable water vapor flux and high quality of effluent during long-term treatments of non-ionic/cationic surfactants and Tween® 20-stabilized oil-in-water (O/W) emulsion in the bench-scale direct contact membrane distillation (DCMD) experiments. The excellent anti-fouling and anti-wetting properties of the Janus membrane were attributed to its hierarchical structured superhydrophilic surface, in which a strong hydration layer was formed and served as an energetic barrier to prevent adsorption of surfactants and oil droplets. Moreover, the electrostatic repulsion between the protonated amino groups on the membrane surface and cationic surfactant molecules also contributed to the robust long-term performance (nearly one-week operation) of the Janus membrane in the treatment of saline water containing cationic surfactant. Our findings reveal the significant role of surface functionality in fouling and wetting resistance of MD membranes and the as-developed Janus membrane shows great potential for water recovery from saline wastewater containing challenging contaminants via DCMD.

Icephobicity and durability assessment of superhydrophobic surfaces: The role of surface roughness and the ice adhesion measurement technique

The durability of anti-wetting properties is of great importance for ensuring long-lasting superhydrophobic and icephobic surfaces that require minimal maintenance and resurfacing. Herein, we fabricated superhydrophobic silicone rubber surfaces having ultra-water repellency and icephobic properties via two industrially applicable methods: micro compression molding (μCM) and atmospheric pressure plasma (APP) treatment. We produced surfaces covered by micro-nanostructures of differing sizes. We evaluated the anti-icing properties (delayed ice formation) and de-icing properties (reduced ice adhesion strength) of the produced surfaces that were subjected to two forms of icing conditions. The well-known ice adhesion measurement techniques, i.e., the centrifuge adhesion and push-off tests, provided quantitative comparisons of the ice adhesion strength of the produced surfaces. We observed two different mechanical deformations during the ice detachment from the surfaces. Although both superhydrophobic surfaces reduced ice adhesion strength, the smaller surface micro-nanostructures produced a greater reduction in ice adhesion by favoring less ice interlocking with the surface asperities. To rigorously assess the durability of the produced surfaces, we carried out a comprehensive series of experiments that covered a wide range of real-life conditions. Under harsh environmental conditions, the surfaces maintained a water contact angle and contact angle hysteresis of >150° and <10°, respectively, thereby confirming the resistance of the superhydrophobic silicone surfaces to severe chemical and mechanical damage. In some cases where water repellency was lost, the silicone rubber surfaces demonstrated a satisfactory recovery of their anti-wetting properties.