Superhydrophobic Polyvinylidene Fluoride Research Articles

F-MWCNTs/AgNPs-coated superhydrophobic PVDF nanofibre membrane for organic, colloidal, and biofouling mitigation in direct contact membrane distillation

While membrane distillation (MD) is considered a promising cost-effective and efficient desalination process, it remains severely affected by membrane fouling that compromises the quantity and quality of water recovered. In this study, superhydrophobic PVDF membranes modified with organically-functionalised silica (f-SiO2) nanoparticles (NPs) were synthesized. Silica nanoparticles (SiO2NPs) were functionalised with three different silane reagents, namely: octadecyltrimethoxysilane (OTMS), N-octadecyltrichlorosilane (ODTS), and chlorodimethyl-octadecyl silane (Cl-DMOS), and finally embedded on polyvinylidene fluoride (PVDF) nanofibre membranes using an in-situ electrospinning technique. The resulting superhydrophobic membranes were coated with a thin layer containing carboxylated multiwalled carbon nanotubes (f-MWCNTs) and silver nanoparticles (AgNPs) to reduce membrane fouling. Fouling tests were conducted using sodium alginate, colloidal silica, and thermophilic bacteria effluent as model organic, inorganic, and bio-foulants, respectively, in direct contact membrane distillation (DCMD). The uncoated membranes were characterized by flux decays ranging from 30 to 90% and salt rejection decays of 1.4–6.1 %. Membrane coating reduced the flux and salt rejection decays to 10–24 % and 0.07–0.75 %, respectively. The hydrophilic coating layer of the nanofibre membrane induced a decrease in the initial water flux (i.e., from 36-42 LMH to 16–17 LMH). However, this coating layer also proved to be efficient in maintaining high salt rejection and resistance to flux decline. This approach is a suitable one-step solution for fouling mitigation in DCMD

Biomimetic superhydrophobic membrane for membrane distillation with robust wetting and fouling resistance

Membrane distillation (MD) is a promising membrane-based thermal process capable of desalinating highly saline water. However, its application is limited by fouling and wetting of commercial hydrophobic membranes. Inspired by the lotus leaf, we developed a biomimetic superhydrophobic polyvinylidene fluoride (PVDF) membrane for robust MD via self-assembly method. The hierarchical micro-nanoscale texture on the membrane surface was constructed by grafting the spherical polyvinylsilsesquioxane (PVSQ) nanoparticles onto micron-sized silica particles (SiPs). The membrane surface energy can be simultaneously lowered due to the hydrophobic groups including vinyls and methoxyls created from the condensation reaction of the vinyltrimethoxysilane (VTMOS). The resulting membrane showed a very high water contact angle (~160°) and a low water sliding angle (<15°), demonstrating the strong hydrophobicity that is expected for a lotus-leaf-like surface. Compared to the commercial PVDF membrane, the fabricated superhydrophobic membrane exhibited superior resistance against wetting by a surfactant (sodium dodecyl sulfate) and fouling by humic acid during MD experiments. Our results suggest that biomimetic superhydrophobic membranes can enhance the operational robustness of MD and facilitate the efficient use of MD for desalinating saline wastewaters in favor of beneficial water reuse and resource recovery.

Patterned superhydrophobic polyvinylidene fluoride (PVDF) membranes for membrane distillation: Enhanced flux with improved fouling and wetting resistance

The industrial implementation of membrane distillation (MD) is still limited due to major barriers such as membrane wetting and low permeate flux. In this study, we fabricated a two-layer patterned superhydrophobic polyvinylidene fluoride (PVDF) membrane by combining non-solvent induced, and vapor induced phase separation processes (NIPS and VIPS), and a subsequent surface fluorination to lower the membrane's surface energy. A simple spacer imprinting method induced changes in the formation mechanism and formed a uniform pattern at the membrane surface increasing the effective surface area and achieving 18% higher flux, compared to a commercial membrane. Moreover, the patterns introduced surface turbulence and favorable flow hydrodynamics that highly improved fouling mitigation when tested in MD with real sweater feed, where the flux was reduced by only 15.2% after 97 h of operation, compared to complete fouling and 100% flux reduction for the commercial membrane. The superhydrophobicity of the developed membrane, characterized by its high water contact angle of 154.5°, also achieved improved wetting resistance when low surface tension surfactant sodium dodecyl sulfate (SDS) was introduced to lower the surface tension of the feed seawater. Our findings indicate the ability of a patterned superhydrophobic membrane surfaces to produce high flux while at the same time enhance fouling and wetting durability, demonstrating their advantage for MD treatment of challenging feeds comprising both fouling and wetting contaminants.

Fabrication of a super hydrophobic polyvinylidene fluoride–hexadecyltrimethoxysilane hybrid membrane for carbon dioxide absorption in a membrane contactor

To obtain a super hydrophobic hollow fiber membrane for using in membrane contact absorption of carbon dioxide (CO2), hybrid polyvinylidene fluoride-hexadecyltrimethoxysilane (PVDF–HDTMS) membranes were fabricated via the non-solvent induced phase-inversion method with ammonia water as the non-solvent additive and dehydrofluorination reagent, and HDTMS as the hydrophobic modifier. The membranes exhibited super-hydrophobicity which was attributed to the formation of rough nanoscale microstructure and low surface free energy of the outer surface. The largest contact angle of water and diethanolamine (DEA) on the membrane outer surface attained 150°. Scanning electron microscopy images revealed that the membrane outer surfaces consisted of rough microscale hierarchical spherulitic particles with a nanoscale stereoscopic coralliform microstructure. Attenuated total reflectance–Fourier transform infrared spectroscopy of the membranes indicated that the HDTMS chains grafted in the PVDF were mainly located on the outer layer of the hollow fiber membranes. The membranes showed excellent CO2 mass transfer flux compared to our previously fabricated membrane with 8 wt % of phosphoric acid as the non-solvent additive in the dope (PVDF-PA-8). The membrane contactor with the membrane obtained by adding 1.5 wt% of HDTMS in the dope achieved the maximum CO2 mass transfer flux of 2.23 × 10−3 mol/m2s with the inlet gas (CO2/N2 = 19/81, v/v) at a flow rate of 20 mL/min and the absorbent liquid (1 mol/L DEA) at a flow rate of 50 mL/min. CO2 mass transfer flux of this membrane decreased by 17% after 17 days of operation and then remained stable.

Scalable fabrication of robust superhydrophobic membranes by one-step spray-coating for gravitational water-in-oil emulsion separation

Hydrophobic anti-wetting membranes have many applications, such as oily wastewater treatment via oil/water separation, desalination via membrane distillation, and carbon capture via gas-liquid membrane contactors. Herein, we used a simple and scalable method to fabricate robust superhydrophobic polyvinylidene fluoride (PVDF) based membranes by one-step spray-coating of fluorinated SiO2 nanoparticles. The prepared PVDF membrane was systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements. The modified PVDF membrane had excellent superhydrophobicity with an extremely high water contact angle up to 171.8 ± 1.1° and a low sliding angle of 1.69 ± 0.13°, due to the fluorinated close-packed hydrophobic SiO2 nanoparticles on the surface. The modified PVDF membrane maintained its relatively stable superhydrophobicity under various harsh conditions, i.e., exposure in hot water, NaOH and HCl, ultrasonication and high-speed flushing, indicating the superior robustness and stability. The prepared membrane also exhibited consistent separation efficiencies up to 99.88 ± 0.03% in water-in-oil emulsions, and superior recyclability and durability over 40 cycles. In addition, spray-coating showed its great promise in engineering various superhydrophobic surfaces on different substrates and excellent scalability in fabricating large-size membranes. This study demonstrates a facilely scalable spray-coating method for engineering robust superhydrophobic surfaces and membranes that can be potentially used for various gas, vapor and water/oil separations.

Enhanced flux in direct contact membrane distillation using superhydrophobic PVDF nanofibre membranes embedded with organically modified SiO2 nanoparticles

AbstractBACKGOUNDMembrane distillation (MD) is a promising low‐cost and efficient desalination process, yet it has not been fully implemented at an industrial scale. Membrane wetting and low porosity are limiting factors leading to low water recovery rates. The current study involved the synthesis of membranes that combined high mechanical stability, porosity and superhydrophobicity, to prevent wetting, with high salt rejection and water flux.RESULTSSilica nanoparticles (SiO2NPs) were synthesized by a novel green chemistry procedure, modified with three different silane reagents [octadecyltrimethoxysilane, N‐octadecyltrichlorosilane (ODTS) and chlorodimethyl‐octadecyl silane] and finally embedded on polyvinylidene fluoride (PVDF) nanofibre membranes using an in‐situ electrospinning technique. These modified membranes displayed a Young's modulus of ∼43 MPa and showed highly porous properties (∼80% porosity, 1.24–1.41 μm pore sizes) and superhydrophobic surfaces (contact angle &gt;150o); thus possessing parameters falling within the range of highly recommended values in MD. Remarkably, the concentration of modified SiO2NPs used to produce the superhydrophobic PVDF nanofibre membranes was significantly lower (1% w/w) than those reported in the literature (3–4% w/w), clearly indicating the efficiency of these silane reagents.CONCLUSIONMembranes embedded with ODTS‐modified SiO2NPs were the most efficient; rejecting salts at high efficiencies (&gt;99.9%) with water fluxes of ≈34.2 LMH at 60 °C, thus indicating their capacity as an energy‐efficient process to produce high purity water. © 2019 Society of Chemical Industry

One-step tailoring surface roughness and surface chemistry to prepare superhydrophobic polyvinylidene fluoride (PVDF) membranes for enhanced membrane distillation performances

Superhydrophobic polyvinylidene fluoride (PVDF) membrane is a promising material for membrane distillation. Existing approaches for preparing superhydrophobic PVDF membrane often involve separate manipulation of surface roughness and surface chemistry. Here we report a one-step approach to simultaneously manipulate both the surface roughness and surface chemistry of PVDF nanofibrous membranes for enhanced direct-contact membrane distillation (DCMD) performances. The manipulation was realized in a unique solvent-thermal treatment process, during which a treatment solution containing alcohols was involved. We demonstrate that by using different chain-length alcohols in the treatment solvent, surface roughness can be promoted by creating nanofin structures on the PVDF nanofibers using an alcohol which has moderate affinity with PVDF. Meanwhile, surface chemistry can be tuned by adjusting the fraction distribution of crystal phases (nonpolar α phase and polar β phase) in the membrane using different alcohols. PVDF membranes with different surface wettabilities were used to evaluate the effects of surface roughness and surface energy on the DCMD performances. Combining both low surface energy and multi-scale surface roughness, pentanol-treated PVDF membrane achieved best anti-water property (water contact angle of 164.1° and sliding angle of 8.1°), and exhibited superior water flux and enhanced anti-wetting ability to low-surface-tension feed in the DCMD application.

Superhydrophobic PVDF nanofibre membranes coated with an organic fouling resistant hydrophilic active layer for direct-contact membrane distillation

Although Membrane Distillation (MD) is envisaged as a promising technology for achieving a cost-effective and sustainable recovery of water from saline solutions, membrane fouling and wetting remain the major challenges that compromise its separation efficiency. To mitigate the high fouling propensities of hydrophobic MD membranes while retaining their high salt rejection efficiencies, superhydrophobic poly-vinylidene fluoride (PVDF) nanofibre membranes embedded with silanized silica nanoparticles (f-SiO2NPs) were synthesised and coated with a hydrophilic active layer containing silver nanoparticles and carboxylated multi-walled carbon nanotubes (AgNPs/f-MWCNTs). While the f-SiO2NPs-modified PVDF nanofibres exclusively allow the transport of water vapour, the AgNPs/f-MWCNTs active provides hydrophilic and biocidal (i.e., biofouling control) properties. The morphology, hydrophobicity, thermal and mechanical properties of the PVDF membranes were rigorously characterized. The PVDF nanofibres were investigated for their resistance to flux decline using a solution containing Bovine Serum Albumin and a real complex effluent containing thermophilic bacteria. f-SiO2NPs-modified PVDF nanofibres showed the highest flux decline (82% after 60 h) associated with BSA adsorption induced by favourable hydrophobic-hydrophobic interactions. AgNPs/f-MWCNTs coated PVDF membranes showed a significant decrease in fouling (47% flux decline) and the highest salt rejections (99.8%). Remarkably, the coating layer showed high biocidal properties towards thermophilic bacteria when subjected to effluent. The current approach provides an important step towards a successful implementation of MD processes at a pilot-scale for water desalting.

Slippery for scaling resistance in membrane distillation: A novel porous micropillared superhydrophobic surface

Scaling in membrane distillation (MD) is a key issue in desalination of concentrated saline water, where the interface property between the membrane and the feed become critical. In this paper, a slippery mechanism was explored as an innovative concept to understand the scaling behavior in membrane distillation for a soluble salt, NaCl. The investigation was based on a novel design of a superhydrophobic polyvinylidene fluoride (PVDF) membrane with micro-pillar arrays (MP-PVDF) using a micromolding phase separation (μPS) method. The membrane showed a contact angle of 166.0 ± 2.3° and the sliding angle of 15.8 ± 3.3°. After CF4 plasma treatment, the resultant membrane (CF4-MP-PVDF) showed a reduced sliding angle of 3.0°. In direct contact membrane distillation (DCMD), the CF4-MP-PVDF membrane illustrated excellent anti-scaling in concentrating saturated NaCl feed. Characterization of the used membranes showed that aggregation of NaCl crystals occurred on the control PVDF and MP-PVDF membranes, but not on the CF4-MP-PVDF membrane. To understand this phenomenon, a “slippery” theory was introduced and correlated the sliding angle to the slippery surface of CF4-MP-PVDF and its anti-scaling property. This work proposed a well-defined physical and theoretical platform for investigating scaling problems in membrane distillation and beyond.

Membrane distillation of saline and oily water using nearly superhydrophobic PVDF membrane incorporated with SiO2 nanoparticles.

Fat, oil and grease in wastewater generated from household kitchens, restaurants and food processing plants affect sewer systems, water resources and environment adversely. Hence, membrane distillation of saline and oily water was studied using a nearly superhydrophobic membrane developed in this work. Polyvinylidene fluoride (PVDF) membrane incorporated SiO2 nanoparticles was synthesized via phase inversion with dual baths and modified using hexadecyltrimethoxy silane. The volume ratio of silane to ethanol was varied between 1:200 to 1:25. The membrane characteristics were examined using a goniometer, a porometer, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The PVDF-SiO2 membrane modified using the volume ratio of 1:50 achieved the highest water contact angle of 141.6° and LEP of 2.642 bar. This membrane was further tested in membrane distillation to observe the permeate flux of distilled water, saline solution (1 M NaCl) as well as saline and oily solution (1 M NaCl; 1,000 ppm of palm oil). The modified PVDF/SiO2 showed high permeate flux which is nearly four times of the permeate flux of neat PVDF membrane, but still susceptible of salt and oil fouling as shown in SEM images.

Hierarchically textured superhydrophobic polyvinylidene fluoride membrane fabricated via nanocasting for enhanced membrane distillation performance

The further advance of membrane distillation (MD) is hampered due to inadequate membrane durability challenged by wetting-induced performance deterioration. The current study presents a novel approach to fabrication of superhydrophobic polyvinylidene fluoride (PVDF) membranes via construction of hierarchical textures on membrane surfaces based on a nanocasting strategy. Two types of PVDF membranes with different surface textures were prepared, separately using a stainless-steel mesh (SSM) or its negative polydimethylsiloxane (PDMS) template as a fabrication substrate. The obtained membranes were systematically characterized in terms of membrane morphology, wetting behavior, MD performance, and antifouling performance. Consequently, the PDMS-based membrane obtained a plaited surface texture, resulting in a high static contact angle of ~153° and a high sliding angle of >90°. The resultant parahydrophobic membrane surface resembled a petal surface. The SSM-based membrane obtained a wave-like pattern, resulting in a high static contact angle of ~164° and a low sliding angle of ~6.8°. The resultant superhydrophobic membrane surface resembled a lotus leave surface. Moreover, both membranes achieved higher water flux and enhanced antifouling performance with no significant compromise in salt rejection. Particularly, the SSM-based membrane achieved the highest flux and best antifouling performance, suggesting promising applications in various fields.

Simplified and robust adhesive-free superhydrophobic SiO2-decorated PVDF membranes for efficient oil/water separation

A simplified adhesive-free strategy for fabricating robust superhydrophobic polyvinylidene fluoride (PVDF) oil/water separation membranes was developed. SiO2 nanoparticles were strongly fixed to the surface of the “adhesive” PVDF membranes via delayed phase inversion. Oil/water filtration membranes with micro–nano coarse structures and low surface energies were obtained by adjusting the SiO2 concentration in a coagulation bath. The membrane structure was analyzed via Fourier transform IR and X-ray photoelectron spectroscopy. The evolution of the morphology, performance of the membranes, and the filtration properties were investigated using scanning electron microscopy and confocal scanning microscopy, among other techniques. The obtained SiO2-nanoparticle decorated PVDF membrane has a water contact angle of 157 ± 2° and an oil contact angle of 0 °. The superhydrophobic PVDF membranes had extremely high chloroform fluxes, over 10,000 L/(m2 h) at 0.9 bar, and could be used for the separation of oil–water mixtures and surfactant-stabilized water-in-oil emulsions. The separation efficiency (approximately 99.95% in terms of the oil purity in the filtrate) was high. Furthermore, the fabricated PVDF oil/water filtration membranes exhibited good stability and excellent recyclability (over 20 cycles). The proposed eco-friendly and straightforward strategy provides new insights for the development of practical oil/water filtration membranes.

Preparation of super-hydrophobic PVDF membrane for MD purpose via hydroxyl induced crystallization-phase inversion

This study aimed to develop an effective method to fabricate super-hydrophobic polyvinylidene fluoride (PVDF) membrane for direct contact membrane distillation (DCMD). Hydroxyl rich silica particle was prepared and added into PVDF dope solution, which was used to prepare super-hydrophobic PVDF membrane via phase inversion method. The influence of the particle on the membrane structure and performance were studied, and the micro-structure forming mechanism of the membranes was researched. It was found that the special spherical micro-structure was formed due to the addition of the hydroxyl rich silica. The spherical micro-structure is mainly composed of γ type crystal, and the transition of PVDF chains from α to γ was induced by the hydroxyl group of the silica particle. Furthermore, the silica particle also acted as the nuclei for crystallization, and the hydrogen bond formed between hydroxyl groups and PVDF chains could facilitate the three-dimensional growth of polymeric spherulites. The pure water contact angle (CA) on the membrane surface reached 153° at the optimum addition (1.5wt%) of hydroxyl rich silica. The MD flux was also enhanced up to 2.7 times of the unmodified membrane.

Superhydrophobic electrospun membrane for heavy metals removal by air gap membrane distillation (AGMD)

This paper presents a novel approach to fabricate superhydrophobic membranes by using environmentally friendly and cost effective superhydrophobic nanoparticles to enhance nanofibrous membrane performance in term of flux and rejection of heavy metals in membrane distillation applications. Polyvinylidene fluoride (PVDF) membranes were fabricated using an electrospinning technique, in which electrospinning parameters such as polymer concentration, voltage, solvent ratio, and cationic surfactant were studied to optimize the membrane fibre diameters and produce beadless nanofibrous membranes. The nanofibrous membranes were characterized in terms of pore size, porosity, liquid entry pressure, contact angle, permeate flux and rejection percentage, and were compared to a commercial membrane. Air gap membrane distillation (AGMD) was used to demonstrate the improved ability of superhydrophobic PVDF membranes for removing heavy metals (such as lead) in comparison with pristine and commercial membranes. The results showed that pristine beadless membrane mat can be fabricated by using 15wt% polymer concentration, 0.05wt% cationic surfactant with 6:4 DMF to acetone ratio and 14 KV with lead rejection rate of 72.77%, liquid entry pressure (17psi) and water contact angle of 132°. In comparison, the composite 11wt% PVDF membranes with 20wt% of functionalized alumina (Al2O3) showed 150° WCA and 27psi as liquid entry pressure which led to 99.36% of heavy metal rejection and 5.9% increase in permeate flux.

Durable and self-healing superhydrophobic polyvinylidene fluoride (PVDF) composite coating with in-situ gas compensation function

A durable and self-healing superhydrophobic polyvinylidene fluoride (PVDF)/polyester-modified silicone resin (PMSR)/microspheric Na2CO3@SiO2 coating with WCA of 158±1.5° and low SA of 4±0.5° has been successfully prepared via sol-gel and spraying technique. After 24h hydrolysis of tetraethylorthosilicate (TEOS), microspheric Na2CO3@SiO2 particles with extremely large storage spaces were obtained as reservoirs for the healing agent of POTS. The superhydrophobicity of the prepared coating can be recovered after 10 rubbing/healing test cycles, indicating the excellent self-healing ability. Simultaneously, the prepared coating also possesses gas compensation capability in acidic condition, which can extend superhydrophobic duration by 400%. The gas compensation capability can be mainly attributed to the bubbles generated from the reaction between acid and porous Na2CO3, hindering water wetting the surface. Moreover, the prepared coating can withstand 4217 friction cycles without obvious surface damage, which is approximately 6 times higher than that of pure PVDF coating. This is mainly due to the combined action of the high adhesion of PMSR, the self-lubrication of PVDF and the surface hierarchical nano/micro wrinkles. The prepared coating also shows prominent superhydrophobic stability under the conditions of acid/alkaline solution (pH=1–14) or strong UV exposure (14days). It is believed that this durable and self-healing superhydrophobic coating is anticipated to open a new avenue to enlarge the application range of superhydrophobic coatings.

Membrane distillation of saline with phenolic compound using superhydrophobic PVDF membrane incorporated with TiO2 nanoparticles: Separation, fouling and self-cleaning evaluation

Superhydrophobic polyvinylidene fluoride (PVDF) membrane was used to study membrane distillation of saline with phenolic compound. Besides addition of TiO2 nanoparticles, superhydrophobic surface of PVDF membrane was created by silane grafting after phase inversion. Three types of silane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) triethoxysilane, (tridecafluro-1,1,2,2-tetrahydrooctyl) triethoxysilane and (3,3,3-trifluoropropyl) trimethoxysilane were used in this work. All the membranes achieved superhydrophobicity (water contact angle >150°), but pore size and porosity were significantly reduced by increasing silane concentration. Lithium chloride (LiCl, 2wt%) was used to improve superhydrophobic PVDF/TiO2 membranes. Membranes were further evaluated in terms of separation performance, fouling tendency and self-cleaning properties. In membrane distillation, all membranes retained 99.9% of the phenolic content in feed (100g/L of gallic acid). However, superhydrophobic PVDF/TiO2 membranes modified using (tridecafluro-1,1,2,2-tetrahydrooctyl) triethoxysilane (1mL silane: 50mL ethanol) and 2wt% of LiCl was the only membrane that maintained the permeate flux near to 6kg.m−2.h−1 without much flux decline after 8h of operation. It also retained 99.9% of sodium chloride (NaCl) and gallic acid simultaneously at a higher feed temperature of 70°C. Although some of these modified membranes were fouled by gallic acid, they could be easily cleaned under UV radiation.

Fabrication of a super-hydrophobic polyvinylidene fluoride hollow fiber membrane using a particle coating process

Membranes with outstanding anti-wetting property are essential for membrane distillation (MD) applications. In this work, a hydrophobization treatment for porous polyvinylidene fluoride (PVDF) hollow fiber membranes using an etching method combined with an ultrafiltration coating process was developed to achieve this desired property. PVDF particle was subjected to an etching process to coarsen its surface. Etched PVDF particles were subsequently dispersed in a dispersant with a specific PVDF-dissolving capacity and then coated onto the PVDF hollow fiber membrane surface via ultrafiltration to construct a super-hydrophobic surface with a micro/nanostructure. After this process, the super-hydrophobic PVDF hollow fiber membrane with the surface contact angle of 163.8°was obtained, and the coating layer on the membrane surface was exceedingly stable. Moreover, the membrane pores were not blocked by the coating layer. The optimal etching conditions for the PVDF particles were as follows: solubility parameter of the etchant, 25.6 (J/cm3)1/2; etching time, 60min at 25°C. A super-hydrophobic surface with a stable particles coated layer is achieved in an optimal coating condition (solubility parameter of the dispersant, 25.87 (J/cm3)1/2; PVDF particles coated, 18.0g/m2). The direct contact membrane distillation (DCMD) experiments showed that after the surface modification process, the hydrophobicity of the membrane was significantly enhanced. In addition, the anti-wetting property of the membrane improved, the time for membrane to be wetted through the channel increased from 40 to 180min, the pure water DCMD flux increased from 26.0 to 29.9kgm−2h−1, and the critical wetting depth increased from 19.5 to 35.7µm.

A robust superhydrophobic PVDF composite coating with wear/corrosion-resistance properties

A robust wear/corrosion-resistant superhydrophobic polyvinylidene fluoride (PVDF)/fluorinated ethylene propylene (FEP)/carbon nanofibers (CNFs) composite coating with a water contact angle (WCA) of 164±1.5° and a slide angle of 5±0.2° has been fabricated through the combination of chemical etching and spraying technique. The WCA of the coating still maintains 141±1.2° after 10,000 times rubbing due to the designed internal nano/micro-structure and the slide angle increases from 5±0.2° to 20±0.5°. The prepared coating also demonstrates excellent corrosion-resistance property under strongly acidic or alkaline conditions for 15 days. The wear-resistance of the superhydrophobic coating is approximately 5 times higher than the pure PVDF coating and commercial fluorocarbon coating. These excellent mechanical properties are attributed to the new groups of CC and CC by dehydrofluorination of PVDF and the new β-phase of PVDF by recrystallization of the α-phase. Furthermore, the enhanced adhesive ability of the coating corresponds with Grade 1 according to GB/T9286, mainly because that the interaction force among PVDF macromolecules can be intensified by chemical cross-linking and the hydroxyl groups formed on the surface of the aluminum plate by etching. It is believed that this robust multifunctional superhydrophobic coating may have the potential values in large-scale application.

A nanocellular PVDF–graphite water-repellent composite coating

We have developed a cost-effective method for the preparation of a porous superhydrophobic polyvinylidene fluoride (PVDF)/graphite composite with an induced nanocellular patterned surface.

Facile synthesis of nano cauliflower and nano broccoli like hierarchical superhydrophobic composite coating using PVDF/carbon soot particles via gelation technique

We have elucidated a cost effective fabrication technique to produce superhydrophobic polyvinylidene fluoride (PVDF/DMF/candle soot particle and PVDF/DMF/camphor soot particle composite) porous materials. The water repellent dry composite was formed by the interaction of non-solvent (methanol) into PVDF/carbon soot particles suspension in N,N-dimethylformamide (DMF). It is seen that longer quenching time effectively changes the surface morphology of dry composites. The nano broccoli like hierarchical microstructure with micro or nano scaled roughen surface was obtained for PVDF/DMF/camphor soot particle, which reveals water contact angle of 172° with roll off angle of 2°. However, composite coating of PVDF/DMF/candle soot particle shows nano cauliflower like hierarchical, which illustrates water contact angle of 169° with roll off angle of 3°. To elucidate the enhancement of water repellent property of PVDF composites, we further divulge the evolution mechanism of nano cauliflower and nano broccoli structure. In order to evaluate the water contact angle of PVDF composites, surface diffusion of water inside the pores is investigated. Furthermore, the addition of small amount of carbon soot particles in composite not only provides the crystallization of PVDF, but also leads to dramatical amendment of surface morphology which increases the surface texture and roughness for superhydrophobicity.