Hierarchical Rough Structure Research Articles

Bio-inspired superhydrophobic fiber membrane for oil-water separation and non-destructive transport of liquids in corrosive environments

Conventional polymer separation membranes or coatings suffer from poor separation performance and serious failure in highly corrosive environments, due to their low chemical and mechanical stability. Herein, a simple electrospraying and electrospinning strategy was used to prepare flexible superhydrophobic carbon fiber membranes (FSCFM). The wettability of FSCFM was improved by forming a lotus leaf-like hierarchical rough structure on its surface. The FSCFM exhibited an excellent permeation flux of immiscible oil-water mixtures (up to 15,800 L m−2 h−1) and water-in-oil emulsions (over 5500 L m−2 h−1), while the separation efficiencies were always kept at more than 99 % after 25 consecutive separations. Even in corrosive environments, its separation performance did not show any degradation. Notably, except for recovering floating oil under external driving forces with excellent cyclic stabilities, FSCFM was also able to transport various corrosive solutions with high efficiencies (99.9 %). After multiple mechanical damages and bending cycles, the FSCFM remained superhydrophobic. It could also maintain its repellency in strong acids/bases, high salt solutions and even under high-temperature environments (94.5 °C). These superior properties make it a strong candidate for oil-water mixture/emulsion separation and non-destructive transport of highly corrosive fluids.

Designing effective underwater self-cleaning surfaces by investigating the oil dewetting ability of hydrophobic and underwater superoleophobic Poly(Diisobutyl Glycolide)-Silica composite surfaces

This study introduces composite thin films of amphiphilic structures to fabricate underwater superoleophobic surfaces. The hydrophobic part of the structure is created by poly(diisobutyl glycolide) thanks to a side chain of isobutyl groups, while the hydrophilic component is formed with hydrophilic silica nanoparticles. Poly(diisobutyl glycolide), having a 77° water contact angle, was obtained through ring-opening polymerization of l-diisobutyl glycolide in a bulk medium, resulting in excellent conversion (97.9 %) and narrow polydispersity (1.47), while maintaining the chiral center. The investigation revealed a notable increment in the underwater hexadecane contact angle from 110° to 160° In contrast, the water contact angle exhibited partial constancy in the air environment because of the augmenting silica content. At a silica content reached up to 30 %, the self-cleaning underwater oil-repellent surface was accomplished, attributable to the phenomenon of the underwater Cassie state, which effectively trapped air within the hierarchical rough structure. Moreover, the surface free energy (SFE) of the composite films was evaluated using both the van Oss-Chaudary-Good and Owens-Wendt methods. Notably, the contact angle of underwater hexadecane decreased with the increase of polar interactions as determined by both methods, owing to the influence of the underwater Cassie state of the hierarchical composite surface.

Formulation and improved properties of three-dimensional superhydrophobic ultra-lightweight fly ash cement foams with C-S-H nanoparticles-stabilized waterproof emulsion

Ultra-lightweight foamed cement (ULFC) is characterized by the super low-density (≤200 kg/m3), excellent thermal-insulation and fire-resistant performance, however, it can inevitably absorb huge amount of water from the surroundings. In this work, a novel three-dimensional superhydrophobic ULFC with apparent density lower than 160 kg/m3 was innovatively achieved by using the bio-inspired design method and C-S-H-nanoparticles-stabilized waterproof emulsion. The results revealed that the water contact angle of ULFC samples can reach up to 154.6°, and the corresponding 24 h volumetric water absorption can be reduced from 8.7 % to 4.1 %. The low-energy organic group of waterproof agents grafted with the surface of hierarchical rough structure in hardened ULFC, which enhanced the hydrophobicity of cement foams.

In-situ grown SiO2 on amino-silane modified polyacrylonitrile nanofibrous membranes and its waterproof-breathable and light-shielding properties

Waterproof and breathable (W&B) materials with light-shielding properties are expected to provide new choices for outdoor clothing. Herein, SiO2@PAN nanofibrous membranes were fabricated by a facile and eco-friendly strategy. Firstly, amino-silane modified polyacrylonitrile (PAN-APS) nanofibrous membranes were prepared by electrospinning. Subsequently, a hierarchical rough structure and robust superhydrophobic surface were formed by a one-step in-situ growing SiO2 and coating with hexadecyltrimethoxysilane (HDTMS). The results showed that SiO2@PAN nanofibrous membranes displayed durable water repellency (the water contact angle above 150° and the sliding angle of about 5.3°), and high breathability (the air permeability of 47.23 mm/s and the moisture permeability of 3.92 kg·m−2·d-1). And SiO2@PAN nanofibrous membranes had a certain durability, which water repellency could maintain even after mechanical abrasion, or after 24 h of immersion in acid-base solutions with pH values of 1, 4, 7, 10 and 13. Moreover, SiO2@PAN nanofibrous membranes showed light-shielding properties. After 10 min exposure to sunlight irradiation, the surface temperature of SiO2@PAN membrane was about 10 °C lower than that of PAN membrane and 20 °C lower than the temperature of the surface without covering membrane. This work provides a promising candidate for protective clothing.

Superhydrophilic and underwater superoleophobic PVDF-PES nanofibrous membranes for highly efficient surfactant-stabilized oil-in-water emulsions separation

Deep oil-water emulsions separation is a challenging task for oily wastewater treatment. Herein, a superwettable nanofibrous membrane was fabricated using the integrated method of electrospinning, microwave-assisted growth, and in-situ polymerization. The membrane possessed superhydrophilicity and underwater superoleophobicity due to the presence of hierarchical rough structures and hydrophilic particles and polymers. The nanofibrous membrane exhibited robust oil-water separation performances for surfactant-free oil-in-water emulsions and different types of surfactant-stabilized emulsions (e.g., SDBS, CTAB and Tween 80) solely under the effect of gravity. The membrane achieved a separation efficiency of >99.94% for surfactant-free oil-in-water emulsions with a flux of 3563.0 L m−2 h−1. The efficiency was above 98.90% with a flux of 1112.5 L m−2 h−1 for SDBS-stabilized oil-in-water emulsion solely under the effect of gravity. The membrane exhibited long-term oil-water separation efficiencies of above 97.0%. Moreover, the membrane showed remarkable stability and can maintain underwater superoleophobicity under different harsh conditions, which is key for large-scale oily wastewater treatment applications.

Improving waterproof-breathable capability of degradable macroporous film/hemp hydroentangled nonwovens composite membranes by porous structure and surface wettability modification

Due to recent serious COVID-19 pandemic, medical protective materials with outstanding microbial barrier and liquid barrier property have attracted much attention. However, the crucial issue of improving the waterproof-breathable capability and degradable properties of medical protective material is still challenging. In this research, poly(butyleneadipate-co-terephthalate) (PBAT)/hemp@silica-polyvinylsilsesquioxane (SiO2-PVSQ) composite membranes with good moisture permeability and waterproof property were fabricated. Firstly, hemp and cotton fibers were mixed and hemp/cotton hydroentangled nonwovens were produced to endow the membranes with outstanding water vapor penetration and mechanical properties. Then, degradable PBAT macroporous membranes were prepared by non-solvent induced phase separation (NIPS) method, and combined with hemp/cotton hydroentangled nonwovens to endow the composite membranes with waterproof property. Finally, SiO2 particles were hydrophobically modified by vinyltrimethoxysilane (VTMOS) and grafted on the surface of PBAT/hemp composite membranes. The waterproof property of composite membranes was further improved by hierarchical rough structure and low surface tension hydrophobic groups on the membrane surface. The prepared PBAT/hemp@SiO2-PVSQ composite membranes showed excellent tensile strength with high moisture permeability, good waterproof and water contact angle of 139.5°, indicating promising candidates for the new generation comfort and degradable medical protective textiles.

Mussel-Inspired Fabrication of an Environment-Friendly and Self-Adhesive Superhydrophobic Polydopamine Coating with Excellent Mechanical Durability, Anti-Icing and Self-Cleaning Performances

Superhydrophobic coatings play a crucial role in self-cleaning and anti-icing infrastructure areas under harsh service environments such as very low temperature, strong wind, and sand impact. In the present study, an environment-friendly and self-adhesive superhydrophobic polydopamine coating inspired by mussels had been successfully developed and its growth process was accurately regulated by formula and reaction ratio optimization. The preparation characteristic and reaction mechanism, surface wetting behavior, multi-angle mechanical stability, anti-icing, and self-cleaning tests were systematically investigated. The results showed that the superhydrophobic coating achieved an ideal static contact angle of 162.7° and a roll-off angle of 5.5° through the proposed self-assembly technique in an ethanol-water solvent. This was due to the coupling effect of constructing a hierarchical roughness structure on the coating surface and reducing its surface energy, which had been well documented by the surface morphology characteristic and chemical structure analysis. The as-prepared coating's self-mechanical performances (tensile strength/shear holding power) and surface wear resistance (sand impact/sandpaper abrasion) behaviors were tested, and results showed tight internal compactness and excellent mechanical robustness, respectively. Furthermore, the 180° tape-peeling on 100 cycles and pull-off adhesion tests indicated that the above coating had significant mechanical stability and an increased percentage (57.4%) of interface bonding strength (27.4 MPa) with steel substrate compared to pure epoxy/steel. This was attributed to the metal chelating capacity between polydopamine catechol moieties and steel. Finally, the superhydrophobic coating had obvious self-cleaning properties by using graphite powder as a contaminant. Additionally, the coating had a higher supercool pressure and displayed much-reduced icing temperature, a longer icing delay time, and an extremely low and stable ice adhesion strength (0.115 MPa) owing to the extreme water-repellence and mechanical durability.

A robust superhydrophobic coating with multi-dimensional micro-nano structure on 5052 aluminum alloy

This paper presents a new method to constructing a robust superhydrophobic surface with multi-dimensional roughness on 5052 aluminum alloy (SHC-Al). The microstructure and surface properties of the SHC-Al were investigated using various techniques including Field emission scanning electron microscope (FESEM), Energy dispersive X-ray spectroscopy (EDS), Laser confocal scanning microscope (CLSM), Fourier transform infrared spectrometer (FTIR), X-ray diffractometer (XRD), Contact angle measuring instrument and electrochemical techniques. The findings indicated that the surface had a hierarchical flower-like micro-nano rough structure, with a water contact angle (WCA) of 162.4° and a rolling angle (SA) of 3.2°, making it easy to clean. Furthermore, the superhydrophobic property can be restored after 90 wear cycles or 33 tape stripping. Electrochemical results demonstrated that the coating had a low corrosion current of 2.742 × 10−9 A·cm−2. The coating remained effective in preventing corrosive mediums from reaching 5052 aluminum surface after soaking in 3.5 wt% NaCl solutions for 72 h, with a coating protection efficiency of 97.9 %, demonstrating excellent anticorrosion properties. Additionally, the coating showed exceptional stability. The results demonstrate that the as-prepared superhydrophobic surface is robust and corrosion-resistant, which hold great promise for practical applications.

Corrosion resistance study of Zn-Ni-B4C composite superhydrophobic coatings with hierarchical rough structure

The composite electrodeposition was used to successfully prepare Zn-Ni-B4C composite superhydrophobic plating with single γ-Ni5Zn21 phase and hierarchical micro/nanostructures on Q235 steel. The addition of micron B4C particles promoted the formation of micron protrusion structures and the change of current density promoted the development of hierarchical rough structures. Electroplated plated layers were electrodeposited at a current density of 5 A·dm−2 for 30 min and modified with an ethanol stearate solution to achieve a water contact angle of 159°, exhibiting excellent superhydrophobicity. Simultaneously, the superhydrophobic plating exhibits good anti-corrosion performance, and the corrosion current density of the plating in 3.5 wt% NaCl solution decreased significantly by 1 order of magnitude compared to the zinc-nickel alloy plating. After 96 h of immersion, the anti-corrosion performance was higher than the untreated Zn–Ni alloy plating, and the plating was still superhydrophobic after modification by stearic acid ethanol solution.

Image analysis of PDMS/ZnO nanocomposite surfaces for optimized superhydrophobic and self-cleaning surface design

Optimized superhydrophobic and self-cleaning nanocomposite surfaces were obtained by spraying surface modified ZnO nanoparticles (NPs) onto PDMS, using octadecylphosphonic acid and octadecanethiol as hydrophobic modifiers. In this study, it is the first time to our knowledge that surface parameters such as topography, morphology, superhydrophobicity, and self-cleaning are correlated to particle surface distribution and agglomeration parameters obtained by image analysis. The topography, morphology, and wettability of the surfaces were analyzed using atomic force microscopy, scanning electron microscopy, static contact angle (SCA), and contact angle hysteresis measurements. Image analysis was performed using the new enhanced graphical user interface of a previously self-developed Matlab® algorithm. Both hydrophobization methodologies increased the NPs’ surface coverage and the hierarchical rough structure formation on the substrates, resulting in more homogenous superhydrophobic self-cleaning surfaces. A higher coated fraction and lower degree of interconnected uncoated PDMS paths are correlated to an increase in SCA. The combination of a higher agglomerates fraction, lower agglomerate radius, and lower distance between agglomerates obtained for the surfaces with hydrophobized ZnO-NPs rendered self-cleaning surfaces. The observed correlations increase the understanding of the design and modelling of superhydrophobic self-cleaning PDMS/ZnO nanocomposite surfaces for use in high voltage outdoor insulators.

Superhydrophobic and Conductive Foams with Antifouling and Oil–Water Separation Properties

Hybrid organic-inorganic materials are attracting enormous interest in materials science due to the combination of multiple advantageous properties of both organic and inorganic components. Taking advantage of a simple, scalable, solvent-free hard-sacrificial method, we report the successful fabrication of three-dimensional hybrid porous foams by integrating two types of fillers into a poly(dimethylsiloxane) (PDMS) framework. These fillers consist of hydrophobic electrically conductive graphene (GR) nanoplatelets and hydrophobic bactericidal copper (Cu) microparticles. The fillers were utilized to create the hierarchical rough structure with low-surface-energy properties on the PDMS foam surfaces, leading to remarkable superhydrophobicity/superoleophilicity with contact angles of 158 and 0° for water and oil, respectively. The three-dimensional interconnected porous foam structures facilitated high oil adsorption capacity and excellent reusability as well as highly efficient oil/organic solvent-water separation in turbulent, corrosive, and saline environments. Moreover, the introduction of the fillers led to a significant improvement in the electrical conductivity and biofouling resistance (vs whole blood, fibrinogen, platelet cells, and Escherichia coli) of the foams. We envision that the developed composite strategy will pave a facile, scalable, and effective way for fabricating novel multifunctional hybrid materials with ideal properties that may find potential use in a broad range of biomedical, energy, and environmental applications.

ZIF-8 based dual scale superhydrophobic membrane for membrane distillation

Hydrophobicity is one of the key factors in determining the permeate flux of membrane distillation. To obtain a high-performance membrane for membrane distillation, a novel preparation method of a superhydrophobic membrane with dual scale hierarchical rough structure was proposed by controlling the particle size of ZIF-8. Nano and micro scale ZIF-8 particles were synthesized by exploring the particle size regulation rules and then deposited on PTFE substrates through the spray method after hydrophobic modification by POTS. The prepared ZIF-8 crystal and modified membrane were analyzed by DLS, SEM-EDS, XRD, AFM, and WCA. The water contact angle of the superhydrophobic surface under optimized experimental conditions reached 165.5°. Furthermore, membrane distillation experiments results of superhydrophobic membrane showed excellent permeate flux than commercial PTFE membrane. This research provides a promising strategy to prepare a superhydrophobic membrane and expands the possibility of MOF as a superhydrophobic coating.

Superhydrophobic polyvinylidene fluoride nanofibrous membranes with stable hierarchical structures for protective textiles

Waterproof and breathable (W&B) membranes, resisting the intrusion of liquid water while allowing transmission of vapor, have been widely applied in various applications. However, there are still great challenges to construct superhydrophobic and mechanically robust W&B membranes. Here, we present a facile strategy to prepare superhydrophobic nanofibrous membranes by combining humidity-induced electrospinning with thermal-pressing treatment. The hierarchical rough structures generated by humidity-induced phase separation of polyvinylidene fluoride jets endow the fiber with superhydrophobicity. Meanwhile, the thermal-pressing manipulation ensures that strong physical bonding exists between nanofibers, which greatly improves the membrane's mechanical and waterproof performances. Significantly, the resulted membranes exhibited desirable superhydrophobicity with water contact angle of 151°, remarkable water and oil intrusion pressures of 81.8 and 36.2 kPa, respectively, high water vapor transmission rate of 7948 g m−2 d−1, and satisfactory tensile strength of 8.1 MPa. The successful development of such membranes provides a new inspiration for the manufacture of superhydrophobic protective membranes.

Fabrication of multifunctional WO3.H2O flower-like micro/nanostructures for the oily wastewater treatment

A multifunctional flower-like WO3.H2O coated mesh with superhydrophilic/underwater superoleophobic properties was fabricated for oily wastewater treatment. The XRD and the FESEM analysis demonstrated the orthorhombic phase and flower-like structure of WO3.H2O. The AFM study confirmed the rough surface structure of the mesh. The mesh displayed outstanding superhydrophilic-underwater superoleophobic behavior. The special wettability of flower-like WO3.H2O mesh may be attributed to its intrinsic high surface energy and hierarchical flower-like rough structure. The mesh with the flower-like structure maintained its excellent underwater oil repellency even after many cycles of different mechanical tests. The consistency in underwater superoleophobicity of the flower-like WO3.H2O coated mesh in different pH and saline environments as well as in long-term storage tests demonstrates its excellent chemical and long-term durability. In addition to the separation of oil-water mixtures with lighter and heavier oils, the mesh can also be employed as a primary unit for emulsion separation. Moreover, the flower-like WO3.H2O coated mesh could also remove efficiently the organic contaminant by the synergistic effect of adsorption and photocatalytic activity. These excellent performances enable the mesh to be employed for sustainable oil-water separation in the practical field.

Electrostatic-modulated interfacial crosslinking and waterborne emulsion coating toward waterproof, breathable, and antifouling fibrous membranes

Developing hydrophobic surfaces for flexible fibrous membranes has attracted tremendous attention for their potential applications in waterproofing, antifouling, and drag reduction. However, conventional methods, such as hydrothermal, coating, and phase separation, often involve complex preparation processes,plugging of porous structures,and heavy use of organic solvents. Herein, a facile and eco-friendly assembly strategy is proposed for fabricating superior hydrophobic surfaces on fibrous membranes. Firstly, a hierarchical rough structure was created on the fiber surface using titanium dioxide nanoparticles as building blocks by a one-pot procedure based on electrostatic complexation and interfacial crosslinking. The procedure is performed in aqueousmedia, at low temperature (50℃) and very fast (∼20 min). Subsequently, a waterborne emulsion was developed by low-surface-energy organosilicon self-assembly in aqueousmedia, which was adopted to coat fiber substrate for surface hydrophobization. The amount of organosilicon is reduced by >90 % of that required in the traditional coating. Consequently, the resultant fibrous membranes exhibit a robust hydrophobic surface with UV-resistant,washdurability, photocatalytic self-cleaning effect, and excellent breathable properties. Besides, this general waterborne hydrophobic coating strategy could be applied to various hydrophilic substrates, including fabrics, aerogels, and sponges. This work provides a novel method to design and fabricate multi-functional hydrophobic surfaces.

Heat Stability and Icing Delay on Superhydrophobic Coatings in Facile One Step.

Superhydrophobic coatings are limited to poor durability and a tedious preparation process. In this work, an efficient, eco-friendly, and cost-effective sol-gel method is developed for preparing superhydrophobic surfaces using an all-in-one suspension composed of methyltrimethoxysilane (MTMS), nano silicon dioxide (SiO2) particles, and micron zinc oxide (ZnO) particles. Superhydrophobic coatings with a contact angle (CA) up to 153.9° and a sliding angle (SA) of about 3.0° are prepared on Q235 steel substrates using MTMS 5 mL, 0.8 g of nano SiO2, and 0.2 g of micron ZnO. The morphology of the superhydrophobic coating is characterized by scanning electron microscopy (SEM), and the surface is covered with a micro- and nano-scaled hierarchical rough structure. A series of tests are conducted, including long-term stability tests and thermostability tests. The CAs are all above 150°, and the SAs are below 6.3°, indicating the excellent static stability of the prepared superhydrophobic coatings. Moreover, the CA of the superhydrophobic coating remains above 152° after 120 h of UV exposure, and the time for a water droplet to freeze on the surface of the superhydrophobic coating is 18 times of the bare Q235 steel, indicating that the superhydrophobic coating exhibits good resistance to UV radiation and icing-delay properties.

Designing Photothermal Superhydrophobic PET Fabrics via In Situ Polymerization and 1,4-Conjugation Addition Reaction.

This study demonstrates a simple and fast method to integrate superhydrophobicity, UV protection, and photothermal effect onto PET fabrics. The surface of PET fabric forms a hierarchical rough structure through in situ oxidative polymerization of the pyrrole (Py). The 1,4-conjugate addition reaction between pentaerythritol tetraacrylate, 3-aminopropyltriethoxysilane, and octadecyl acrylate not only endows the PET fabric with superhydrophobicity but also forms a cross-linked network structure which improves the stability of multifunctional coatings on the surface of the PET fabric. In addition, the wettability of the prepared PET fabric is investigated by adjusting the Py monomer and octadecyl acrylate concentration. The results reveal that the prepared PET fabrics exhibit obviously superhydrophobic behavior with a contact angle of 155.8°. The surface temperature of the superhydrophobic PPy/PET fabric can rise to 91 °C under a simulated sunlight which is much higher than the pristine PET fabric, while reaching basically the same steady-state in five heating/cooling cycles. The prepared PET fabric also possesses excellent self-cleaning, UV shielding, and solar light absorption performances. Furthermore, the superhydrophobic PET fabric exhibited excellent stability against 180 °C high temperature, strong UV radiation, different pH solutions and organic solvent erosion, 8 h washing tests, and 25 sandpaper abrasion cycles. These findings provide a path for the future development of multifunctional fabrics using fluorine-free environmentally friendly materials.

Corrosion Resistance Study of Zn-Ni-B4c Composite Superhydrophobic Coatings with Hierarchical Rough Structure

Corrosion Resistance Study of Zn-Ni-B4c Composite Superhydrophobic Coatings with Hierarchical Rough Structure

Fabrication of superhydrophobic surfaces with hierarchical structure and their corrosion resistance and self-cleaning properties

Mixed SiO2 nanoparticles with different ratios and contents were dispersed in hydrophobic fluorinated/silanized polymers. The mixture was bonded to the A3 steel substrate with an adhesive to obtain a superhydrophobic surface with excellent performance. The appearance, hardness, adhesion, and surface wettability of the obtained coatings with different ratios of mixed nanoparticles were characterized. Then, a series of superhydrophobic coatings with good hardness, adhesion, and crack-free surfaces were selected for further systematic investigation. The results showed that the coatings with contact angle around 151° ∼x223C 157° can be obtained when the hydrophobic polymer is combined with different proportions of mixed nanoparticles. The surface chemical composition of these coatings changed little while the surface structure changed significantly. The mixing ratios of nanoparticles had a significant effect on the surface morphology and sliding angle. Smaller nanoparticles had a greater impact on superhydrophobic coating performance than larger nanoparticles. Moreover, the mechanical robustness and corrosion resistance of the superhydrophobic coatings regularly changed with the proportions of smaller nanoparticles. Water droplets are easy to roll on the surface of the superhydrophobic coating with hierarchical rough structure, which makes it possesses an excellent self-cleaning performance.

Cellulose nanospheres coated polylactic acid nonwoven membranes for recyclable use in oil/water separation

Oily wastewater has always been an environmental issue that we are concerned about and committed to managing. Although the superwetting membranes have been extensively studied and widely used in oil/water separation, the abundant discarded membranes are still headaches due to their non-degradable nature. In this work, all-around green material, as well as superhydrophilic polylactic acid (PLA) nonwoven membrane, is designed by coating cellulose nanospheres (CNCs) with the aid of polydopamine (PDA). Plenty of hydroxyl groups and hierarchical rough structure synergistically contribute to the superhydrophilicity and excellent oil/water separation performance of the resultant CNCs/PDA/PLA nonwoven membrane. Interestingly, the efficiency of oil/water separation can be maintained above 98% after 100 times of repeated use. With the outstanding durability and easy controllability, the CNCs/PDA/PLA nonwoven membrane may provide effective solutions to manage the oily wastewater and secondary pollution of the used membrane itself simultaneously.Graphic abstract