Superhydrophobic Fabrics with Mechanical Durability Prepared by a Two-Step Plasma Processing Method

Plasma-Induced Superhydrophobicity as a Green Technology for Enhanced Air Gap Membrane Distillation

Superhydrophobicity has only recently become a requirement in membrane fabrication and modification. Superhydrophobic membranes have shown improved flux performance and scaling resistance in long-term membrane distillation (MD) operations compared to simply hydrophobic membranes. Here, we introduce plasma micro- and nanotexturing followed by plasma deposition as a novel, dry, and green method for superhydrophobic membrane fabrication. Using plasma micro- and nanotexturing, commercial membranes, both hydrophobic and hydrophilic, are transformed to superhydrophobic featuring water static contact angles (WSCA) greater than 150° and contact angle hysteresis lower than 10°. To this direction, hydrophobic polytetrafluoroethylene (PTFE) and hydrophilic cellulose acetate (CA) membranes are transformed to superhydrophobic. The superhydrophobic PTFE membranes showed enhanced water flux in standard air gap membrane distillation and more stable performance compared to the commercial ones for at least 48 h continuous operation, with salt rejection >99.99%. Additionally, their performance and high salt rejection remained stable, when low surface tension solutions containing sodium dodecyl sulfate (SDS) and NaCl (down to 35 mN/m) were used, showcasing their antiwetting properties. The improved performance is attributed to superhydrophobicity and increased pore size after plasma micro- and nanotexturing. More importantly, CA membranes, which are initially unsuitable for MD due to their hydrophilic nature (WSCA ≈ 40°), showed excellent performance with stable flux and salt rejection >99.2% again for at least 48 h, demonstrating the effectiveness of the proposed method for wetting control in membranes regardless of their initial wetting properties.

How Different Are Fog Collection and Dew Water Harvesting on Surfaces with Different Wetting Behaviors?

As the clean water shortage becomes a serious problem for mankind, atmospheric water harvesting has emerged as a viable solution. Two main approaches to collect water from the atmosphere exist: the first is to capture it from fog, whereas the second is through condensation of vapor on surfaces with a temperature below the dew point. The water collection mechanism in these two modes is completely different. In this work, we develop a deeper understanding of the effect of surface wettability on gravity-assisted atmospheric water harvesting and a comparative study of the two collection modes (fog and dew). First, we present theoretical estimates for the maximum water mass available in each mode and introduce an efficiency factor η which enables the direct comparison among surfaces in different setups and modes. Then we fabricate a series of micronanostructured surfaces with different surface wetting properties from hydrophilic to superhydrophobic. Our results demonstrate that drop mobility, derived from the surface superhydrophobic properties and micronanotopography, is the most important factor affecting fog collection: superhydrophobic surfaces show 40-65% higher fog collection rates compared to flat hydrophilic surfaces, with the more mobile among superhydrophobic surfaces (hysteresis 2°, and air-liquid fraction f_A-L > 0.9) showing higher water collection. On the other hand, dew harvesting efficiency depends on the combination of drop mobility and nucleation rate, with superhydrophobic surfaces exhibiting 40% higher water collection rate compared to the flat hydrophilic or hydrophobic surfaces due to their low hysteresis as well as high surface area available for nucleation.

Developing Super-Hydrophobic and Abrasion-Resistant Wool Fabrics Using Low-Pressure Hexafluoroethane Plasma Treatment

The growing interest in wool fibres as an eco-friendly and sustainable material for diverse industrial applications requires an enhancement of their functional performance. To address this, wool fabrics were treated in the present research with low-pressure hexafluoroethane (C₂F₆) plasma to impart superhydrophobicity and improve their abrasion resistance. Unscoured and scoured wool fabrics were treated with C₂F₆ while varying plasma power (80 W and 150 W), gas flow rate (12 sccm and 50 sccm) and treatment time (6 min and 20 min), and the effect of plasma parameters on the abrasion resistance, water contact angle and dyeing behaviour of the wool fabrics was studied. Martindale abrasion testing showed that the surface abrasion of the wool fabrics increased with the number of abrasion cycles, and the samples treated with 150 W, 20 min, 12 sccm showed superior abrasion resistance. The scoured wool fabrics showed a contact angle of ~124°, which was stable for only 4 min 40 s, whereas the plasma-treated samples showed a stable contact angle of over 150°, exhibiting a stable superhydrophobic behaviour. The C₂F₆ plasma treatment also significantly reduced the exhaustion of an acid dye by wool fabrics. The EDX study confirmed the deposition of fluorine-containing elements on the wool fabrics significantly altering their properties.

Robust Superhydrophobic and Repellent Coatings Based on Micro/Nano SiO2 and Fluorinated Epoxy

Superhydrophobic surfaces possess low mechanical strength, and can be easily contaminated by fluids with low surface tension, such as oil; this hinders their practical applications. In this study, fluorinated epoxy was prepared through the thiol-ene click reaction at first. The superhydrophobic surface with high oil-repellency was prepared by the addition of unmodified nano-SiO2 and micron-SiO2 to the fluorinated epoxy. The effect of the ratio of micro- and nano-silica particles on the morphology and wettability of the coating was investigated. It was shown that a re-entrant structure appears and FEP-S coating has good liquid repellency when the amounts of nano-SiO2 and micro-SiO2 are equal. The contact angles of the FEP-S coating (coating with the best liquid repellent performance) for water, glycerol, ethylene glycol, and diiodomethane were 158.6° ± 1.1°, 152.4° ± 0.9°, 153.4° ± 1.3°, and 140.7° ± 0.9°, respectively. In addition, the superhydrophobic coatings possess excellent mechanical and chemical durability, excellent performance in self-cleaning, corrosion resistance, and anti-icing properties. The preparation method of superhydrophobic coating is relatively simple; therefore, it has a wide range of applications and can also be applied to various substrates.

Fabrication of Robust Water-Repellent Technology on Cotton Fabric via Reaction of Thiol-ene Click Chemistry

A robust superhydrophobic fabric coating was fabricated on cotton fabric under UV light, which was achieved by convenient surface modification with mercaptopropyltriethoxysilane, tetramethyltetravinylcyclotetrasiloxane, and octadecyl mercaptan. The modification of cotton fabric with 3-mercaptopropyltriethoxysilane introduces reactive mercapto groups, after which 2,4,6,8-tetramethyltetravinylcyclotetrasiloxane reacts with mercapto groups, and octadecyl mercaptan provides microscale roughness. The nonpolar carbon chains of thiol cause the cotton to have a low surface energy. As reported, the combination of microscale roughness with low surface energy has a superhydrophobic effect on cotton, which leads to a high contact angle of 161.8° and sliding angle of 8°. Infrared spectroscopy, XPS, and SEM tests were used to characterize the chemical structure and morphological changes of the surface of cotton fabric before and after click reaction. The fabric after click reaction exhibited an oil–water mixture separation ability owing to its superhydrophobicity. Thus, the finished fabric could be used in the oil–water separation field. Importantly, the superhydrophobic textile displays resistance to laundering, mechanical abrasion, strong acidic and alkaline environments, and UV irradiation. We hope that this study can broaden the real-life applications of cotton fabric.

Surface Modification of Fumed Silica by Plasma Polymerization of Acetylene for PP/POE Blends Dielectric Nanocomposites

Novel nanocomposites for dielectric applications-based polypropylene/poly(ethylene-co-octene) (PP/POE) blends filled with nano silica are developed in the framework of the European ‘GRIDABLE’ project. A tailor-made low-pressure-plasma reactor was applied in this study for an organic surface modification of silica. Acetylene gas was used as the monomer for plasma polymerization in order to deposit a hydrocarbon layer onto the silica surface. The aim of this modification is to increase the compatibility between silica and the PP/POE blends matrix in order to improve the dispersion of the filler in the polymer matrix and to suppress the space charge accumulation by altering the charge trapping properties of these silica/PP/POE blends composites. The conditions for the deposition of the acetylene plasma-polymer onto the silica surface were optimized by analyzing the modification in terms of weight loss by thermogravimetry (TGA). X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray fluorescence spectroscopy (EDX) measurements confirmed the presence of hydrocarbon compounds on the silica surface after plasma modification. The acetylene plasma modified silica with the highest deposition level was selected to be incorporated into the PP/POE blends matrix. X-ray diffraction (XRD) showed that there is no new crystal phase formation in the PP/POE blends nanocomposites after addition of the acetylene plasma modified silica. Differential scanning calorimetry results (DSC) show two melting peaks and two crystallization peaks of the PP/POE blends nanocomposites corresponding to the PP and POE domains. The improved dispersion of the silica after acetylene plasma modification in the PP/POE blends matrix was shown by means of SEM–EDX mapping. Thermally stimulated depolarization current (TSDC) measurements confirm that addition of the acetylene plasma modified silica affects the charge trapping density and decreases the amount of injected charges into PP/POE blends nanocomposites. This work shows that acetylene plasma modification of the silica surface is a promising route to tune charge trapping properties of PP/POE blend-based nanocomposites.

Fabrication of a Conjugated Fluoropolymer Film Using One-Step iCVD Process and its Mechanical Durability

Most superhydrophobic surface fabrication techniques involve precise manufacturing process. We suggest initiated chemical vapor deposition (iCVD) as a novel CVD method to fabricate sufficiently durable superhydrophobic coating layers. The proposed method proceeds with the coating process at mild temperature (40 °C) with no need of pretreatment of the substrate surface; the pressure and temperature are optimized as process parameters. To obtain a durable superhydrophobic film, two polymeric layers are conjugated in a sequential deposition process. Specifically, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4D4) monomer is introduced to form an organosilicon layer (pV4D4) followed by fluoropolymer formation by introducing 1H, 1H, 2H, 2H-Perfluorodecyl methacrylate (PFDMA). There is a high probability of covalent bond formation at the interface between the two layers. Accordingly, the mechanical durability of the conjugated fluoropolymer film (pV4D4-PFDMA) is reinforced because of cross-linking. The superhydrophobic coating on soft substrates, such as tissue paper and cotton fabric, was successfully demonstrated, and its durability was assessed against the mechanical stress such as tensile loading and abrasion. The results from both tests confirm the improvement of mechanical durability of the obtained film.