Fluoroalkylsilane Research Articles

Green kaolin-tailored hydrophobic composite membrane for efficient desalination of high-salinity water

This study reports a novel approach to tune the surface and activate ceramic-polymeric based membranes from widely available and naturally occurring kaolin materials for the desalination of highly saline water via membrane distillation. Electrospraying was used to endow the membrane surface with a fine distribution of silica particles to build on roughness and enhance the grafting of long-chain (F21) fluoroalkyl silane (FAS). Interestingly, the adopted approach significantly transformed the surface properties from hydrophilic with water contact angle WCA ∼ 40° to superhydrophobic nature with WCA ∼ 160° along with significant increase in the liquid entry pressure. In air-gap membrane distillation with 70,000 ppm NaCl feed solution, the developed membranes exhibited a stable salt rejection (∼ 99.99 %) and a high water permeate flux of 9.3 kg/m2h. Notably, the membranes developed via the adopted approach outperformed direct FAS-modified kaolin membranes and other reported ceramic-based membranes. Hence, electrosprayed silica and subsequent FAS treatment approach on the membrane surface can effectively activate and make way for actual applications of the ceramic-based membranes for the desalination of highly saline water.

High-performance, superhydrophobic, durable photonic structure coating for efficient passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is an innovative and energy-free cooling technology that automatically cools the surface of an object by reflecting sunlight and emitting heat into outer space without the need for external energy inputs. However, PDRC materials often face issues such as surface contamination and poor long-term outdoor durability. Herein, a photonic structure coating with high PDRC performance, superhydrophobic property, and high outdoor durability was designed and prepared using a phase separation strategy. The photonic structure coating achieves a solar reflectance ∼97.6 % and an average atmospheric window (AW) emissivity of ∼93 %. Under direct sunlight (800 W/m2), the coating exhibits good PDRC performance, with an average temperature drop of ∼13 °C and a maximum temperature drop of up to ∼20 °C. The rough and porous surface of the coating can adsorb air, reducing the solid-liquid adhesion and endowing the coating with super-hydrophobic properties. The incorporation of a small amount of fluoroalkyl silanes into the coating provides water resistance, resulting in a water contact angle (WCA) of ∼155.1° and sliding angle (SA) of ∼2.3°, meeting the need for self-cleaning. Furthermore, the coating exhibits superior durability, including resistance to acid and alkali, UV aging, abrasion, and scratching. All these merits render this photonic structure coating great potential for real-world applications.

Fouling-resistant superhydrophobic polyketone membranes modified with fluorine-containing silica for water-in-oil emulsion separation

Membranes for water-in-oil (W/O) emulsion separation require high emulsion permeance, oil purity selectivity, high water-fouling resistance, and reusability. Therefore, a functional membrane structure that satisfies these needs is required. Herein, we describe the effective modification of a membrane surface by forming functional silica particles on a porous polyketone (PK) membrane to form a hierarchical membrane structure with enhanced roughness and superhydrophobicity. We also demonstrate the potential application of the membrane for W/O emulsion separation based on enhanced performance and fouling resistance. Membranes were fabricated by forming silica particles on a porous PK membrane by a sol–gel method using tetraethoxysilane (TEOS). By modifying these silica particles with fluoroalkyl silane (FAS), a superhydrophobic membrane with a high contact angle of up to 162° was fabricated. The resulting FAS-modified membrane had higher permeance with regard to a toluene W/O emulsion than an unmodified PK membrane or a commercially available polyvinylidene fluoride (PVDF) membrane. It was possible to recycle the FAS-modified membrane by simply washing it in toluene to remove external fouling. This effective membrane surface modification helps to enhance both emulsion permeance and fouling resistance during W/O emulsion separation.

Elucidating the interaction between polar alkoxysilane-modified silicate glass and ionic surfactant in the obtainment of hydrophobic transparent film

Soda-lime-silicate glass is a widely used material in industry and everyday life. For some applications, it is important to have hydrophobic properties of its surface and at the same time retain the transparency in the visible spectrum. This can be achieved using fluoroalkyl silanes as surface modifiers. However, fluorine shows severe health effects and the nowadays tendency is to use more appropriate substances for surface modification. In this work, we show the possibility of obtaining a hydrophobic and transparent film on silicate glass using alkoxysilanes with alkyl groups possessing terminal -NH2 and subsequent modification of such silanized glass using an anionic surfactant. The possible mechanism of the interaction between the chemisorbed silyl group and the dodecyl sulfate ion was discussed.

Super hydrophobic self-stratified coating based on epoxy terminated polyurethane/siloxane nano-composite

ABSTRACT Recently, the application of superhydrophobic coatings on insulators has emerged as an effective strategy for mitigating risks and damages. In the current investigation, a superhydrophobic coating formulated with polyurethane (PU) prepolymer and polydimethylsiloxane (PDMS) has been developed, featuring a surface layer of SiO2 nanoparticles (NPs) modified with fluoroalkyl silane (FAS). The identification of peaks within the ranges of 567, 650, 747, and 898 cm− 1, corresponding to CF, CF₂, and CF₃ bonds, along with the reduction of the peak associated with the hydroxyl group around 3433 cm− 1, substantiates the interaction between FAS13 and SiO2 nanoparticles. The resultant coating exhibited a 39% increase in hydrophobicity compared to the coating without nanoparticles. The surface modification of nanoparticles resulted in an escalated degradation rate for the USMN sample, reaching a temperature range of 300 to 400°C. This phenomenon is attributed to the interaction between the hydroxyl groups on the nanoparticle’s surface and the Si-O bonds present in the FAS13 composition, leading to increased thermal resistance of the nanoparticle. This study successfully produced a PDMS/PU coating utilizing modified SiO2 particles through a self-stratified approach. This coating acts as an adhesive layer for high-voltage insulation surfaces, effectively protecting against water intrusion and dust accumulation.

Chemical Instability-Induced Wettability Patterns on Superhydrophobic Surfaces.

Chemical instability of liquid-repellent surfaces is one of the nontrivial hurdles that hinders their real-world applications. Although much effort has been made to prepare chemically durable liquid-repellent surfaces, little attention has been paid to exploit the instability for versatile use. Herein, we propose to create hydrophilic patterns on a superhydrophobic surface by taking advantage of its chemical instability induced by acid solution treatment. A superhydrophobic Cu(OH)2 nanoneedle-covered Cu plate that shows poor stability towards HCl solution (1.0 M) is taken as an example. The results show that 2.5 min of HCl solution exposure leads to the etching of Cu(OH)2 nanoneedles and the partial removal of the self-assembled fluoroalkyl silane molecular layer, resulting in the wettability transition from superhydrophobocity to hydrophilicity, and the water contact angle decreases from ~160° to ~30°. Hydrophilic dimples with different diameters are then created on the superhydrophobic surfaces by depositing HCl droplets with different volumes. Afterwards, the hydrophilic dimple-patterned superhydrophobic surfaces are used for water droplet manipulations, including controlled transfer, merging, and nanoliter droplet deposition. The results thereby verify the feasibility of creating wettability patterns on superhydrophobic surfaces by using their chemical instability towards corrosive solutions, which broadens the fabrication methods and applications of functional liquid-repellent surfaces.

The effects of carbon ion implantation on wettability, abrasion, thermal and anti-corrosion stabilities of laser ablated super-hydrophobic Nitinol surface

Comparing with pure laser irradiation, the hybrid fabrication using laser ablation and chemical modification is one of the widely used techniques to obtain bio-inspired super-hydrophobic surface. Nevertheless, conventional surface chemical modification techniques have faced challenges including the detachment of micro-nano structures and the instability of super-hydrophobic surfaces. This research introduces an innovative method for creating extremely stable super-hydrophobic surfaces on NiTi alloy through a combination of laser exposure, carbon ion implantation, and modification with fluoroalkylsilane (FAS). Surface morphology and chemical component were systematically investigated to reveal the formation mechanism of super-hydrophobicity. Besides, its abrasion stability, thermal stability and corrosion resistance stability of this kind of super-hydrophobic surface were also investigated. And the corresponding stability improvement mechanisms were further revealed.

Development of Janus membranes with asymmetric wettability for desalination of impaired seawater by direct contact membrane distillation

Membrane distillation (MD) is an emerging technology for direct seawater desalination. The widely employed hydrophobic membranes are susceptible to pore wetting/ fouling in the presence of organic contaminants in seawater. Here, we demonstrate a facile method of preparing Janus membranes with hydrophilic/hydrophobic faces having excellent anti-fouling and anti-wetting properties. The hydrophobic substrate is a PVDF-co-HFP membrane incorporating fluoroalkylsilane (FAS) grafted hydrophobic MIL-53(Al)- a form of metal organic framework (h-MIL-53(Al)), and the hydrophilic coating is prepared by the direct deposition of polydopamine (PDA) (top layer). The optimum membrane exhibited a stable flux of 11 L/m2h and permeate conductivity ∼10 µS/cm for up to 60 h of seawater desalination. The anti-wetting property of the Janus membrane was demonstrated from the stable performance when challenging the membrane with impaired seawater containing low surface tension compounds such as sodium dodecyl sulphate (SDS) and propylene glycol (PG), and oil (hexadecane). The prepared membrane exhibited wetting resistance of 45 h and 18 h when feed was seawater containing 0.3 mM SDS and 3 wt% PG, respectively. The membrane displayed excellent resistance to fouling for desalination from SDS-stabilized hexadecane (500 ppm)/seawater feeds for up to 50 h (5 cycles). The membrane fabricated in this study holds the potential for seawater desalination.

Self-repairing superhydrophobic microfiber leather leveraging light-triggered release of actives

Microfiber-composed functional synthetic leather is of particular interest because it owns the advantages of good fluffiness, softness, excellent hygroscopicity, the random three-dimensional bundle structure similar to that of natural leather, which grants excellent moisture permeability, air permeability, chemical resistance, waterproof and mildew resistance, and various functions. Typically, the microfiber of functional synthetic leather is obtained through splitting the original sea-island fiber by solvent-induced dissolution and etching of its sea phase, which inevitably leads to the decline of the wettability of the treated leather. Herein, light-triggered functional microcapsules for self-healing wettability of split microfibers have been judiciously designed and developed. These functional microcapsules loaded with fluoroalkyl silane, which are used to coat onto the original sea-island fiber, allow for photocontrol of releasing the superhydrophobic chemical to the coated fibers. Despite the superhydrophobicity of the split fiber would be weakened by the splitting operation, the light-triggered release of fluoroalkyl silane can effectively amend its superhydrophobic properties. The microfiber leather self-repaired by the functional microcapsules exhibits good superhydrophobic performance, excellent self-cleaning ability to dust and RhB solution, high friction resistance (up to 200 rubs), and good UV light self-repairing cycle performance. This study provides a versatile solution for efficiently self-repairing microfiber leathers after the splitting process.

Evaluation of the Water Repellency and Structure of Cellulose Nanofibers Derived from Waste Hop Stems Using a Fluoroalkyl Silane Coupling Treatment

Evaluation of the Water Repellency and Structure of Cellulose Nanofibers Derived from Waste Hop Stems Using a Fluoroalkyl Silane Coupling Treatment

Mechanically robust superhydrophobic polyurethane coating for anti-icing application

The development of superhydrophobic coatings with excellent mechanical properties is essential for effective anti-icing protection. In this study, we achieved a durable superhydrophobic anti-icing coating by introducing the nanosilica, co-modified with fluoroalkyl silane and aminosilane, into polyurethane through a simple spraying and curing process. The resulting coating had a water contact angle (CA) of up to 162° and a sliding angle (SA) less than 1.5°. We enhanced the mechanical and chemical durability of the coating by reacting amino groups on the silica surface with the isocyanate groups in the curing agent. The coating maintained its superhydrophobicity even after 200 cycles of sandpaper abrasion, 24 h of water impact, or 500 ml of falling sand impact. Additionally, the coating exhibited excellent anti-icing performance, delaying the water-freezing time to 700 s at −15°, and the ice-adhesion strength remained lower than 13 KPa after 25 icing-deicing cycles. These results suggest that the durable superhydrophobic coatings can effectively prevent long-term icing, making them as promising anti-icing candidates for various applications in polar ships.

Construction of NaHCO3 fire extinguishing agent modified by fluoroalkyl silane containing short fluorocarbon Chain: Improve its anti-reignition performance

Construction of NaHCO3 fire extinguishing agent modified by fluoroalkyl silane containing short fluorocarbon Chain: Improve its anti-reignition performance

Hierarchically Branched Siloxane Brushes for Efficient Harvesting of Atmospheric Water.

Atmospheric water harvesting is considered a viable source of freshwater to alleviate water scarcity in an arid climate. Water condensation tends to be more efficient on superhydrophobic surfaces as the spontaneous coalescence-induced droplet jumping on superhydrophobic surfaces enables faster condensate removal. However, poor water nucleation on these surfaces leads to meager water harvest. A conventional approach to the problem is to fabricate micro- and nanoscale biphilic structures. Nonetheless, the process is complex, expensive, and difficult to scale. Here, the authors present an inexpensive and scalable method based on manipulating the water-repellent coatings of superhydrophobic surfaces. Flexible siloxane can facilitate water nucleation, while a branched structure promotes efficient droplet jumping. Moreover, ToF-SIMS analysis indicated that branched siloxane provides a better water-repellent coating coverage than linear siloxane and the siloxanes comprise hydrophilic and hydrophobic molecular segments. Thus, the as-prepared superhydrophobic surface, TiO2 nanorods coated with branched siloxanes harvested eight times more water than a typical fluoroalkylsilane (FAS)-coated surface under a low 30% relative humidity and performed better than most reported biphasic materials.

Surface modification strategy for controlling wettability and ionic diffusion behaviors of calcium silicate hydrate

Solid substrates of cementitious composites served in high salinity and humidity environments are invariably covered by a layer of fluid water. Thus wetting behavior of cement hydrates is critical to their durability due to calcium leaching. Meanwhile, chloride ingress phenomena are highly dependent on it. These effects severely aggravate the microstructural degradation of calcium silicate hydrate (C-S-H), with mechanisms that are pronounced at molecular level. Here, we investigate here the nanoscale wetting behaviors of C-S-H and report a surface modification strategy to control its hydrophobicity. Molecular dynamic simulation results reveal that the surfactant, fluoroalkylsilane (FAS), furnishes superhydrophobic surfaces, which hinders ionic interactions and stabilizes the interlayer calcium to eliminate calcium leaching in C-S-H. Further, FAS layer provides a rougher and highly electronegative surface, blocking the chloride adsorption and invasion. This work portrays atomistic insights in C-S-H surface properties, improving the chemical and physical stability of cementitious composites in saline solutions and providing strategies for their surface modifications.

Improving the Efficiency of Hydrogen Spillover by an Organic Molecular Decoration Strategy for Enhanced Catalytic Hydrogenation Performance

Hydrogen migration from metal particles to the support, known as hydrogen spillover, has provided insights for designing highly efficient catalysts in catalytic processes involving hydrogen. A facile and controllable strategy is highly desired to achieve an effective hydrogen spillover effect on nonreducible oxides for catalytic performance optimization and clarifying the catalytic function of hydrogen spillover. Here, we provide an organic molecular decoration (OMD) strategy obtained by the molecular layer deposition-like pulse method for facilitating hydrogen spillover over the nonreducible silica support. After decorating with the fluoroalkylsilane (FAS) molecular layer, the hydrogen spillover effect over the catalysts (xFAS-Pt/SBA-15) is greatly enhanced due to the presence of carbonaceous species compared with the original Pt/SBA-15. The amount of hydrogen spillover can also be precisely regulated by controlling the FAS pulse number. For cinnamaldehyde hydrogenation, xFAS-Pt/SBA-15 presents superior catalytic performance versus its untreated counterpart and the sample decorated via the traditional method. Also, the catalytic activity varies based on the FAS pulse number, showing a linear correlation with the amount of hydrogen spillover. The altered adsorption behavior of the reactant plays an important role in the hydrogenation selectivity. This facile OMD strategy for efficient hydrogen spillover is general and may have potential applications in many heterogeneous reactions.

Fluoroalkylsilane grafted FeOOH nanorods impregnated PVDF-co-HFP membranes with enhanced wetting and fouling resistance for direct contact membrane distillation

Direct contact membrane distillation (DCMD) is a versatile thermal-driven membrane separation technique that can be used for seawater distillation and water recovery. Initially, the central composite design was used to optimize the concentration/molecular weight of pore former and operating feed/permeate flow rates. Further, a dual modification strategy was used to fabricate robust hydrophobic polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) membranes- (i) incorporation of fluoroalkylsilane (FAS) grafted FeOOH nanorods (F-g-FeOOH) into the membrane and (ii) surface coating of the membrane with FAS. The membrane with 0.015 wt% FeOOH nanorods (M2) displayed the highest water contact angle (132 ± 1.6ᵒ) with more than 99.98% salt rejection for 10,000 ppm NaCl solution (ΔT= 60 ℃ & feed/permeate flow rate = 20 L/h). The M2 membrane exhibited stable performance, and no pore wetting could be observed even when the feed contained polyhydric alcohol (5 wt% propylene glycol) or surfactant (80 ppm sodium dodecyl sulfate). The M2 membrane also displayed a stable permeate flux of 3.5 L/m2h and a total organic carbon rejection > 96% for up to 12 h for a saline feed (10,000 ppm NaCl) containing hexadecane/water emulsion (100 ppm oil). The prepared membranes were also determined to be suitable for long-term seawater desalination and exhibited a stable permeate flux of 10 L/m2h for 60 h with permeate conductivity < 5 µS/cm. The facile fabrication strategy holds the potential to be further explored to prepare membranes with excellent anti-wetting and anti-fouling properties.

Investigating the performance of surface-engineered membranes for direct contact membrane distillation

ABSTRACT Direct contact membrane distillation (DCMD) is an emerging technology gaining attraction in seawater desalination and concentration of aqueous solutions. In this study, a facile surface modification strategy using hydrophobic ZIF-8 and a fluoroalkylsilane (FAS) was employed to improve the performance of commercial PVDF and PVDF/PTFE blend membranes. The PVDF/PTFE membrane modified using 10 wt./vol % hydrophobic ZIF-8 and 1 H, 1 H, 2 H, 2 H-perfluorooctyltriethoxysilane (PFOTES) exhibited the highest water contact angle (121 ± 4.7°), improved surface roughness (51.6 ± 1.4 nm), most significant vapor flux (17.6 ± 2 L/m2h), and salt rejection of 99.98% with 10,000 ppm NaCl synthetic feed solution at the optimum operating conditions. The surface-engineered membranes exhibited excellent anti-fouling (360 minutes) and anti-wetting performance (240 minutes) when challenged with saline feed solution containing 50 ppm sodium alginate solution and 0.1 mM sodium dodecyl sulfate, respectively. The surface engineered membranes produced permeate of uniform quality for>10 h and could recover~31% water during actual seawater desalination (10 h). Moreover, these membranes could concentrate propylene glycol by a factor of 1.24 within 6 h and retain>80% of it. This facile surface modification strategy holds an excellent potential to be further explored for commercial applications.

Exploring durability and environmental impact of cementitious composites modified by fluoroalkyl-silane based additive

This article focuses on an original molecular pathway to predict the durability and analyze the environmental impact of fluoroalkyl-silane (FS) based additive modified cementitious composites in marine environment. The key is to reveal the calcium leaching behaviors of cement composites through molecular simulation, then evaluate the porosity and chloride diffusion coefficient, which determines their lifespan. Simulation results indicate that decalcification can be eliminated through FS surface modification, decreasing the porosity, and slowing down chloride accumulation. Then we map the simulation findings to their environmental impact by quantitatively analyzing the lifespan of a cement cover in marine environment. It is demonstrated that 0.762 wt% FS is the optimal mixing content, which significantly reduces the repair frequencies. In such a condition, 52.33 % CO2 emissions and 31.07% non-renewable energy consumption can be diminished. Our findings portray an atomic understanding for improving the durability of cement composites and propose strategies to predict their service life and environmental impact.

Growing nearly vertically aligned ZnO nanorod arrays on porous α-Al2O3 membranes to enhance the separation of MTBE from aqueous solution

The separation of methyl tertiary butyl ether (MTBE) from aqueous solution by pervaporation-based membrane technology has attracted much attention recently. The present work proposed a novel strategy to enhance the MTBE/water separation performance of porous α-Al2O3 membranes. ZnO seeds were planted on the surface of α-Al2O3 membranes by the deposition and decomposition of zinc acetate, followed by growing ZnO nanorod arrays (ZNA) on the seeded α-Al2O3 membranes by hydrothermal reaction in the mixed hydrated zinc nitrate (HZN) and hexamethylenetetramine (HMTA) solution. Finally, the membranes were hydrophobized by grafting fluoroalkylsilane (FAS) onto their surface. The results show that the MTBE/water separation factor has been dramatically promoted from 7.7 for the α-Al2O3 membranes to 55.7 for the ZNA-covered α-Al2O3 membranes. The promotion may be attributed to the nearly vertically aligned ZnO nanorod arrays, which provide much surface area to load more fluorocarbon groups that are amiable to MTBE molecules and supply a superhydrophobic surface. The MTBE in the permeate mixture has been concentrated to as high as 72.9 wt%, in striking contrast to 4.6 wt% in the feed solution. The obtained membranes are highly stable upon long-term operation.

In-situ fabrication of superhydrophobic surface on copper with excellent anti-icing and anti-corrosion properties

The accumulation of ice on electrical construction works not only leads to the reduced efficiency of power supply and heat exchangers, but also increases the energy losses and even brings about serious disasters. Therefore, it is essential to reduce or eliminate the issue of ice accumulation on metal constructions. Nowadays, superhydrophobic surfaces have received lots of attentions for their outstanding hydrophobicity. In this study, Cu(OH)2 nano grass was firstly in-situ constructed on copper surface via simple anodization, then superhydrophobic CuO nano needles were obtained after the dehydration of Cu(OH)2 and modification with fluoro-alkyl silanes. The results showed that when the anodic oxidation temperature was 20 °C and the current density was 2 mA·cm−2, nano-needle-like multistage micro-nano structures can be obtained. The as-prepared superhydrophobic surface showed the water contact angle as large as 162° and sliding angle lower to 4°. Additionally, the as-prepared superhydrophobic surface displayed outstanding anti-icing property, delaying icing substantially even under − 10 °C environment regardless of droplet volume and type. Moreover, it also revealed good anti-corrosion property with a corrosion current density of 2.2 × 10−8 Ω·cm2 and the corrosion resistance of 1.55 × 106 Ω·cm2 which is about three order of magnitudes than that of bare copper. We prospect that this easily prepared surface can provide a solution of anti-icing and anti-corrosion for electrical construction works and large-scale metals.