Hydrophobic Surface Layer Research Articles

Innovative 3D Janus foam design achieves high-efficiency and stable solar desalination with improved salt resistance and heat management

SDIE technology is an effective means to address freshwater scarcity, but faces challenges such as thermal management, salt scale resistance, and high energy efficiency. Herein, a 3D Janus Foam with a hydrophobic surface layer and a hydrophilic inner layer was synthesized for efficient seawater desalination. Such strategic layering provides effective thermal management, resulting in a heat loss of only ∼1.13 % throughout the photothermal conversion process. The Janus Foam’s ability to prevent salt accumulation while maintaining high evaporation efficiency over extended periods is a critical improvement over current technology. Under 1 kW m−2, the evaporation rate of the Janus Foam is as high as 1.7898 kg m−2 h−1 with an efficiency of 96.87 %. Even under actual seawater conditions, the evaporation rate of the foam remains at 1.7426 kg m−2 h−1 with an efficiency of 91.83 %, demonstrating its high energy efficiency and adaptability to different operating environments. In conclusion, the innovative design of the 3D Janus foam offers a promising avenue for addressing global freshwater scarcity through enhanced solar interfacial evaporation processes.

Chemical and UV Durability of Hydrophobic and Icephobic Surface Layers on Femtosecond Laser Structured Stainless Steel

Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study investigates their durability against acetone, ethylene glycol, and UV radiation. The laser-structured surfaces were immersed in the respective liquids for up to 48 h. The results indicate limited durability of the superhydrophobic and icephobic layers when submerged in acetone and ethylene glycol, with more favorable results for petrol treatment than vacuum treatment. Similar results were obtained after 100 h of UV exposure, showing a decrease in superhydrophobic properties and an increase in ice adhesion. However, repeated vacuum treatments conducted after the chemical durability tests revealed the potential for partial recovery of the hydrophobic and icephobic properties. XPS analysis was performed throughout the experiments to evaluate changes in surface chemistry resulting from the post-laser treatments and the durability tests.

Highly Moisture-Resistant Flexible Thin-Film-Based Triboelectric Nanogenerator for Environmental Energy Harvesting and Self-Powered Tactile Sensing.

Triboelectric nanogenerator (TENG) has been demonstrated as a sustainable energy utilization method for waste mechanical energy and self-powered system. However, the charge dissipation of frictional layer materials in a humid environment severely limits their stable energy supply. In this work, a new method is reported for preparing polymer film as a hydrophobic negative friction material by solution blending poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and polyvinyl chloride (PVC), doping with titanium dioxide (TiO2) nanoparticles, and further surface patterning modification. The P-TENG composed of the PVDF-HFP/PVC/TiO2 composite film with optimized hydrophobic performance (WCA = 124°) achieved an output voltage of 235 V and a short-circuit current of 35 μA, which is approximately three times that of the bare PVDF-HFP-based TENG. Under charge excitation, the transferred charge of the P-TENG can reach 35 nC. When the external load resistance is 5.5 MΩ, the output peak power density can reach 1.4 W m-2. Meanwhile, the hydrophobic surface layer with a rough surface structure enables the device to overcome the influence of water molecules on charge transfer in a humid environment, quickly recover, and maintain a high output. The P-TENG can effectively monitor finger flexibility and strength and realize real-time evaluation of the exercise state and hand fatigue of the elderly and rehabilitation trainers. It has broad application prospects in self-powered intelligent motion sensing, soft robotics, human-machine interaction, and other fields.

Novel dual-layer ZIF-71/PH-PSF electrospun nanofiber for robust membrane distillation

Membrane distillation (MD) is a promising technology for the treatment of hypersaline dyeing wastewater. However, commercial membranes still have limitations such as low permeate flux, membrane fouling, and membrane wetting issue in MD process. Herein, a dual-layer MD membrane was fabricated with a polysulfone (PSF) bottom layer and a poly(vinylidene fluoride-co-hexafluoropropylene) (PH) hydrophobic surface layer incorporated with ZIF-71 nanoparticles. The addition of ZIF-71 was optimized based on the results of surface morphology, contact angle, and MD performance. The incorporation of ZIF-71 nanoparticles into PH nanofiber membranes, along with their dual-layer structure, has led to notable improvements in both permeate flux and rejection performance. The fouling resistance of membrane was further evaluated with model dyeing wastewater as feed solution, which contained four types of dyes and heavy metal antimony. The MD performance of the optimized membranes was also measured with real dyeing wastewater as feed solution. The dual-layer membrane decorated with ZIF-71 nanoparticles significantly outperformed the pristine membrane in treating real dyeing wastewater, exhibiting potential for practical applications. Finally, the underlying mechanism on the improved permeate flux and rejection was elucidated systematically.

Hydrophobic polyvinyl butyral/polytetrafluoroethylene composite coating on 5052 aluminum alloy: Preparation, characterization, and anticorrosive properties

To enhance the corrosion resistance of metal, the current investigation employed polyvinyl butyral (PVB) as the intermediate bonding layer and polytetrafluoroethylene (PTFE) as the hydrophobic surface layer to prepare a PVB/PTFE composite coating on the surface of 5052 aluminum alloy (5052AA) through a simple dipping and pulling method. The optimum preparation process, microstructure, surface characteristics and anticorrosion properties of the PVB/PTFE/5052AA were characterized and analyzed by means of field emission scanning electron microscope (FESEM), confocal laser scanning microscope (CLSM), contact angle measuring instrument and electrochemical techniques. The findings showed that the optimal preparation process involved a PVB dosage of 0.7 g, a PTFE mass fraction of 20 %, and a sintering temperature of 150 °C. The surface of PVB/PTFE/5052AA presented a morphology of interwoven nanobelts, with a water contact angle (WCA) of 133.8° ± 0.4°, indicating the transformation from hydrophilic to hydrophobic. Furthermore, the composite coating exhibited good chemical stability, mechanical robustness, and its surface could be transformed from hydrophobic to superhydrophobic after tape peeling. Electrochemical studies revealed that the low-frequency |Z| value of PVB/PTFE/5052AA was higher than 108 Ω·cm2, and the phase angle was close to −90° over a wide frequency range. Moreover, after being immersed in NaCl solution for 48 h, the water absorption of the composite coating remained at a low level of about 2.7 %. These results demonstrate that PVB/PTFE is a promising composite coating with broad application potential.

Multi-weather full-body triboelectric garments for personalized moisture management and water energy acquisition

The occurrence of extreme events (such as heatwaves, heavy precipitation) is unprecedented in the observed record and will increase with increasing global warming, leading to severe human health issues. Wearing suitable garments in different weather is one of the solutions for people to ease their physical discomfort in an energy-saving way. However, only one piece of traditional clothes hardly satisfies the demand of the changing weather. Herein, a multi-weather full-body triboelectric garment with a one-way moisture transport structure is presented to keep people feeling cool in the scorching weather while capturing droplet energy in rainy situations. A trilayer progressive wetting structure was designed to effectively transport sweat from the inner layer near the skin to the outer layer to keep the skin dry and comfortable in the muggy air, with a unidirectional transmission index of 1025%. When it starts to rain, the rain droplets quickly roll down the textile surface and generate triboelectric energy with the hydrophobic surface and conductive MXene layer inside. More than that, the scalable fabrication process makes it possible to obtain the textile with enough areas for making a whole garment, which is much more practical in real application scenarios.

Robust superhydrophobic magnetic melamine sponge inspired by lotus leaf surface for efficient continuous oil–water separation

Inspired by the oily surface layer and hierarchical structure on the lotus leaf surface, a magnetic sponge with robust superhydrophobicity (water contact angle up to 155°) and surface protection was synthesized by one-pot solvothermal method by introducing (3-Mercaptopropyl)trimethoxysilane into the melamine sponge. After hydrolysis and self-polymerization, (3-Mercaptopropyl)trimethoxysilane can grow as a low surface energy polysiloxane coating on the surface of sponges and magnetic particles. It not only provides a hydrophobic surface layer for sponges, but also this cooperation of micro-submicron-nanostructure from micron sponge skeleton, submicron Fe3O4 particles and nanoscale polysiloxane builds rough surfaces at multiple scales. Based on the triadic Koch curve model, the theory of superhydrophobic surface is elucidated in detail from the surface fractal behavior, fractal dimension, and surface composition. The sponge can be integrated into a negative pressure system as a filter element for continuous and efficient oil–water separation. The formed polysiloxane can not only provide protection for the sponge skeleton and magnetic particles, but also provide strong cross-linking between the two materials, which can effectively resist the damage to the functional structure caused by oil erosion. In addition, a conceptual diagram of a portable oil suction device similar to a vacuum cleaner was proposed. Combining the basic theory of robust superhydrophobic surface and innovatively clarifying the influence of filter element structure on oil–water separation efficiency from the perspective of interface force, it is expected to bring more practical and potential ideas for the design of a portable vacuum cleaner-like oil–water separation device.

Lignin emulsifying rosin for improved sizing performance and mechanical properties of liquid packaging board

Global liquid packaging industry has been greatly spurred by the rapidly growing food & beverage industry all over the world. Liquid packaging board (LPB), as the main composition (75–80 %) of laminated liquid packaging cartons, must possess high-quality of hydrophobicity and physical properties for excellent leak-proof and protecting the packaged commodity. Herein, in this study, lignin is selected to prepare lignin cationic surfactant (LCS) by quaternary ammonium modification. Then cationic lignin modified rosin size ( L -CDRS) with uniform microsphere structure and high colloidal stability is successfully synthesized via a phase inversion process to improve the sizing performance and mechanical properties of LPB. The cation modified LCS presents improved amphipathicity of rich cationic charges and hydrophobic benzene ring skeleton, thus enhancing the electrostatic interactions between LCS and pulp fibers and improving the sizing performance of L -CDRS. The sizing performance of LPB is evaluated by varying the LCS dosages within L -CDRS and concluded that the edge penetration value and Cobb value of LPB handsheets exhibit an improved size performance with 2 % LCS within L -CDRS, implying the formation of homogeneous hydrophobic surface layer induced by the well-distribution of L -CDRS. In addition, the tensile index of LPB increased from 19.74 N·m/g to 25.96 N·m/g assisted by 2 % LCS emulsified L -CDRS, indicating an improved mechanical property. This study puts forward a practical and facile strategy to improve the sizing performance and mechanical properties facilitated by lignin enhanced rosin size and will further broaden the application range of traditional rosin size and lignin in LPB products. • Lignin was modified into quaternary ammonium etherified cationic surfactant with improved emulsifying ability. • Cationic lignin can emulsify rosin to prepare L -CDRS with uniform microsphere structure and high colloidal stability. • L -CDRS exhibited a significantly improved sizing performance of LPB compared with the control rosin size. • The addition of L -CDRS contributed greatly to the enhanced mechanical properties of LPB. • The mechanism of improved sizing performance and mechanical properties of LPB induced by L -CDRS size agent was proposed.

Liquid-liquid microextraction with hydrophobic deep eutectic solvent followed by magnetic phase separation for preconcentration of antibiotics

This study describes a miniaturized approach for liquid-liquid microextraction based on mass transfer into low volume of deep eutectic solvent and magnetic phase separation, using specially produced magnetic chromium dioxide nanoparticles with a hydrophobic surface layer of fatty acids. The nanoparticles modified with fatty acid helped to recover low volumes of viscous hydrophobic deep eutectic solvent-based extract reproducibly and easily (up to 10 μL) in a microextraction procedure with the application of magnetic forces. It was demonstrated that the collector properties depend on nanoparticles’ surface and magnetic characteristics. The developed approach was implemented for the separation and preconcentration of trace fluoroquinolone antibiotics from environmental waters prior to their determination by high-performance liquid chromatography with fluorometric detection as a model analytical task. The limits of detection, calculated from a blank test based on 3σ, were 0.01 μg L−1 for ofloxacin, 0.02 μg L−1 for lomefloxacin and fleroxacin, and 0.04 μg L−1 for norfloxacin. The procedure provides significant solvent reduction and high enrichment factors. The approach is green, which is proved by the analytical eco-scale assessment tool with the total score equal to 85 out of 100.

Biomimetic hydrophilic foam with micro/nano-scale porous hydrophobic surface for highly efficient solar-driven vapor generation

Solar-driven vapor generation by localized solar heating of a photothermal material is an environmentally friendly approach for seawater desalination and wastewater purification. In this work, inspired by the leaf transpiration in nature, we designed a novel bionic leaf to realize highly efficient solar vapor generation. The leaf-inspired three-dimensional (3D) material structure had a hydrophilic polyvinyl alcohol (PVA) foam layer (equivalence to the mesophyll tissue layer in a leaf) with high porosity and low thermal conductivity, a photothermal polypyrrole (PPy) layer (equivalence to the chlorophyll layer in a leaf) coated on the PVA foam, and a micro/nano-scale porous hydrophobic surface layer (equivalence to the stomal layer in a leaf). The PVA network had microchannels for water transportation and reducing water evaporation enthalpy, the PPy layer absorbed and converted solar energy to heat water locally, and the hydrophobic porous surface layer enhanced the rate of vapor escape. The asfabricated vapor generator based on the bionic-leaf structure achieved an impressive high evaporation rate of 3.09 kg m−2 h−1 under one sun irradiation (1 kW m−2). The prototype vapor generator desalinated and purified brine and seawater successfully under natural sunlight. Such solar vapor generator based on the biomimetic structure provides a potential low-cost and highly efficient water purification technology to help mitigate the global water crisis using sustainable energy.

Tuning Microenvironment of Quaternary Ammonium Salt and Tertiary Amine Bifunctionalized Polyacrylonitrile Fiber for Cooperatively Catalyzed Aza-Michael Addition

A series of novel polyacrylonitrile fiber catalysts modified with different ratio of quaternary ammonium salt (QA) to tertiary amine (TA) were screened for heterogeneously catalyzed aza-Michael addition in water. The best catalyst was found to be PANPQ-1F with a QA:TA ratio of 1:1, which can lead to high yield, excellent selectivity of solvent and great recyclability under optimized conditions. The special microenvironment of hydrophilic inner layer and hydrophobic surface layer of PANPQ-1F is conducive to the leaving of the product and the high conversion of the reaction. Based on the fact that appropriate microenvironment combined with the catalytic sites promoted the reaction, cooperative effect of QA and TA in the microenvironment of PANPQ-1F catalyst was proposed.

Surface modification of poly(vinyl alcohol) fibers to control the fiber-matrix interaction in composites

Polymeric fibers with varied acid/base behavior and wettability were prepared to control fiber-matrix interactions in fiber-reinforced composites. Water-insoluble high-performance poly(vinyl alcohol) fibers were equipped with different surface functionalities on a molecular level by chemical bonding of aldehydes and adsorption of acidic and alkaline polyelectrolytes. The fibers were characterized by surface-sensitive methods, such as X-ray photoelectron spectroscopy, zeta potential, and contact angle measurements. The modification resulted in stable thin nonpolar layers or polar acidic, alkaline, and amphoteric surface functionalities on the fiber surface, with advancing contact angles of deionized water between 30° and 90°. Fiber-matrix interactions were probed by pullout tests of single fibers embedded in a cementitious matrix and subsequent morphological analysis of the fibers. Polar surface functionalities caused a strong fiber-matrix adhesion while nonpolar, hydrophobic surface layers decreased the adhesion dramatically. The surface charge and acid/base behavior of the fibers had no significant influence.

Quantum-Chemical Model of the Structure of Iron Silicate Polysulfide

The spatial structure of iron silicate polysulfide is simulated and its stability is evaluated Using the Priroda 6 quantum-chemical software and the Chemcraft visualization program. The high strength of bonds regardless of the lengths of sulfuric chains is confirmed theoretically, testifying to iron’s ability to retain long sulfuric chains with no weakening of bonds. It is found that iron chloride acts as bridges between silica gel clusters and sulfur with the formation of iron silicate polysulfide, which can be used to obtain building materials. It is shown that sulfur can form hydrophobic surface layers on such materials that protect them from being destroyed in aqueous media. It can also form dense nonporous materials.

Surface modification of ZnO nanowire arrays with PTFE and their wettability property

Super-hydrophobic materials are important for their self-cleaning function which has become an increasingly popular research topic. This special surface in biologic world with super-hydrophobicity gives us a lot of inspiration to produce artificial hydrophobic materials to be applied in daily life and industry. Coating polytetrafluoroethylene (PTFE) on ZnO nanowire arrays is believed an ideal structure to produce a super hydrophobic surface layer. However, it is still a challenge to well combine PTFE and ZnO nanowires with high durability by a simple method. In this paper, we studied the wettability property of the surface modified ZnO nanowire arrays. These vertically ordered and well crystallized ZnO nanowire arrays were synthesized by a microwave-assisted hydrothermal method. After coating a thin layer of PTFE on those ZnO nanowire arrays by a simple vapor deposition method, the surface of samples has excellent super hydrophobicity with extremely low water rolling angle. The experimental results testify the modified ZnO nanowires have a good self-cleaning surface.

ESTIMATION OF THE SLIP LENGTH IN THE FLOW OF LIQUID IN MICRO-CHANNELS

Research review of phenomenon for slip flow in micro and nanocannels is presented in the paper. The analysis of theoretical and experimental data characterizing the slip length is carried out. In slip flow in microchannels the slip length is affected by the contact angle of the liquid with the surface, shear stress, pressure, dissipative heating, the amount and nature of the dissolved gas in the liquid, electrical characteristics, surface roughness. Studies of flow in microchannels with hydrophobic walls, which are based on molecular dynamics, showed that the slip length has order of 20 nm. This is much less than the values observed in the experiment. The introduction of an effective (apparent) slip length suggests the existence of a thin layer of gas bubbles near the hydrophobic surface or liquid layer with low value of viscosity and density. Since the idealized model for the total coverage of a hydrophobic surface by gas bubbles gives, as a rule, overestimated values of the slip length in comparison with experimental ones, some researchers consider the inhomogeneous coating of the wall by gas bubbles. In this case, the effect of a layer with a lower viscosity on the slip length turns out to be weaker.

Enhancement of the stability of green-emitting Ba2SiO4:Eu2+ phosphor by hydrophobic modification

This paper proposes a simple and feasible surface modification method to suppress the moisture-induced degradation of the green-emitting phosphor Ba2SiO4:Eu2+ (BSO:Eu2+), which hits its reliability very hard and restricts its wide commercialization in WLEDs. A hydrophobic surface layer was formed on the surface of this phosphor via hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The produced surface layer consisted of an amorphous silicon dioxide with a thickness of ∼2nm along with the presence of −CH3 groups on the surface. The modified phosphor featured superior stability in high-pressure water steam conditions at 150°C.

Highly Stable Red‐Emitting Sr2Si5N8:Eu2+ Phosphor with a Hydrophobic Surface

One of the biggest problems in white light‐emitting diodes (WLEDs) is the moisture‐induced degradation of phosphors. This paper proposes a simple and feasible surface modification method to solve it, whereby a hydrophobic surface layer is developed on the surface of the phosphors. The particular case of orange‐red‐emitting Sr2Si5N8:Eu2+ (SSN) phosphor was investigated. The mechanism to develop the hydrophobic layer involves hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The experimental results showed that the surface layer of SSN phosphor was successfully modified to a hydrophobic nanolayer (8 nm) of amorphous silicon dioxide that contains CH3 groups in the surface. This hydrophobic surface layer gives the modified phosphor superior stability in high‐pressure water steam conditions at 150°C.

(Industrial Electrochemistry and Electrochemical Engineering Division Student Achievement Award) Engineering the Ionic Polymer Phase Surface Properties of a PEM Fuel Cell Catalyst Layer

During high power density operations, the performance of polymer electrolyte membrane fuel cells (PEMFCs) is limited by high water saturation levels in the cathode catalyst layer due to high wettability of the ionic polymer phase. A new heat treatment was used to create and permanently lock-in the surface structure of a biphasic membrane (Nafion® 212). Several surface characterization techniques were used to verify the engineered membrane’s surface after heat treatment, including contact angle, multi-mode atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We found that specific heat treatment conditions will lead to the formation of either a hydrophobic or hydrophilic surface layer. The results of this research will guide the design of a new class of PEMFC catalyst layers. Engineered PEMFC catalyst layers are expected to prevent electrode flooding, therefore leading to higher performance and efficiency during high power density operations.

Titanium oxide – reduced graphene oxide – silver composite layers synthesized by laser technique: Wetting and electrical properties

Electrically conductive and highly hydrophobic surface layers are attractive for many practical applications. In this work the functional, wetting and electrical properties of titanium dioxide (TiO2), TiO2/silver (Ag), and TiO2/reduced graphene oxide (rGO)/Ag nanocomposite coatings layers are reported. The functional properties of the layers were correlated with their chemical composition and bonding states between the constituent elements, determined in turn by the synthesis and immobilization process parameters. The nanocomposite coatings were obtained by matrix assisted pulsed laser evaporation, a laser-based environmental friendly thin film deposition technique. The synthesized ternary TiO2/rGO/Ag coatings has optimum performances, highly hydrophobic character and low electrical resistance, attributed to the presence of Ag nanoparticles and to the reduction of the oxygen containing functional groups of the GO platelets during laser irradiation and transfer processes leading to the formation of graphene-like material.

Coalescence of Water Drops in Water-ULSD Dispersions via Electrowetting

Coalescence of water droplets is an important phenomenon in many industrial applications. One approach for coalescing water droplets is by applying an external voltage across the drops. Coalescence occurs when spreading and motion of the drops due to the electrical field brings the drops into contact. Electrowettable surfaces were prepared with poly(styrene-co-methyl methacrylate) as the dielectric film and Fluropelâ„¢ as the hydrophobic surface layer. The surface of a stainless steel disk was coated in a way that the dielectric coating layer thickness varied with radial position with minimum thicknesses at the center and at the outer edge of the disk and a maximum at an intermediate radial position of the disk surface. The thickness gradient influenced the droplet movement and contributed to the coalescence. Two disks were assembled with a thin slit between the disks. Emulsions of water droplets in ultra low sulfur diesel fuel were pumped through the thin slit. Experiments showed significant increase in drop sizes when the disks were electrified compared to non-electrified disks.