Superhydrophobic Silica Nanoparticles Research Articles

Mechanically robust and durable polyurethane-based superhydrophobic coating containing silica nanoparticles derived from hydrothermal assisted sol–gel method

In the current study, a suspension of hydrothermal assisted sol–gel synthesised superhydrophobic silica nanoparticles (h-SNPs) are sprayed over apartially cured polyurethane (PUR) surface on aluminium substrate. The surface exhibited superhydrophobic (SH) property with a water contact angle of 166 ± 2° and awater sliding angle of < 5°. X-ray diffraction study confirmed the formation of amorphous silica nanoparticles. The particle size determined by field emission scanning electron microscope is about 19–21 nm. The roughness of the coating is 3.5 µm as characterised using a surface profilometer. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy investigations indicated the presence of urethane linkages from PUR and siloxane stretching from h-SNPs. The adhesion of the coating tested with a cross-hatch cutter as per ASTM D3359 shows a rating of 5B. The coating qualified mandrel bend test conducted according to ASTM D255. No cracks are observed at the deformed areas and water drops roll off the surface, demonstrating the integrity of the coating and its superhydrophobicity. The coating exhibits high robustness as evident from sandpaper abrasion and tape peel tests. When compared to superhydrophobic polyurethane (SH PUR) coating developed using commercial silica as reported in our previous work, the developed h-SNPs coating is much more durable as confirmed by accelerated weathering test and anti-icing test. The SH coating also exhibits superhydrophobicity even after 200 h of accelerated weathering test and 16 de-icing cycles. The coating withstands 15 days of water immersion and also displays self-cleaning property.

Environmentally friendly SLIPS coating based on flexible sponge: A novel approach to antifouling for ships

To mitigate the attachment of fouling organisms, Slippery Liquid-Infused Porous Surfaces (SLIPS) hold tremendous potential as a green and broad-spectrum antifouling solution, capable of replacing traditional antifouling coatings. However, the complexity of current preparation methods and the limited lifespan of lubricating oils constrain their widespread application in marine antifouling for vessels. In this study, melamine sponge (MS) was used as a substrate, and modifications were made by introducing superhydrophobic silica nanoparticles (SiO2 NPs), a biocompatible adhesive (ethyl cyanoacrylate, ECA), and a highly stretchable polymer (poly-ε-caprolactone, PCL). By combining natural surface microstructures with additional nanomaterials, we successfully obtained a superoleophilic surface, effectively capturing liquid lubricants and maintaining their long-term stability. The sponge substrate possesses distinctive contractility, with the lubricant stored in the grid spontaneously compensating for the loss of surface lubricant, thereby effectively enhancing its durability. This study provides a straightforward fabrication method with reduced manufacturing costs for environmentally friendly marine anti-fouling coatings. The approach demonstrates a prolonged cyclic anti-fouling effect, effectively advancing the development of SLIPS for anti-fouling applications in shallow marine environments.

Superhydrophobic silica nanoparticles produced from rice husks, wettability at the macro- and nanoscale

Superhydrophobic silica nanoparticles produced from rice husks, wettability at the macro- and nanoscale

Scalable Fabrication of Superhydrophobic Coating with Rough Coral Reef-Like Structures for Efficient Self-Cleaning and Oil-Water Separation: An Experimental and Molecular Dynamics Simulation Study.

Superhydrophobic coating has a great application prospect in self-cleaning and oil-water separation but remains challenging for large-scale preparation of robust and weather-resistant superhydrophobic coatings via facile approaches. Herein, this work reports a scalable fabrication of weather-resistant superhydrophobic coating with multiscale rough coral reef-like structures by spraying the suspension containing superhydrophobic silica nanoparticles and industrial coating varnish on various substrates. The coral reef-like structures effectively improves the surface roughness and abrasion resistance. Rapid aging experiments (3000h) and the outdoor building project application (3000 m2 ) show that the sprayed superhydrophobic coating exhibits excellent self-cleaning properties, weather resistance, and environmental adaptability. Moreover, the combined silica-coating varnish-polyurethane (CSCP) superhydrophobic sponge exhibits exceptional oil-water separation capabilities, selectively absorbing the oils from water up to 39 times of its own weight. Furthermore, the molecular dynamics (MD) simulation reveals that the combined effect of higher surface roughness, smaller diffusion coefficient of water molecules, and weaker electrostatic interactions between water and the surface jointly determines the superhydrophobicity of the prepared coating. This work deepens the understanding of the anti-wetting mechanism of superhydrophobic surfaces from the perspective of energetic and kinetic properties, thereby paving the way for the rational design of superhydrophobic materials and their large-scale applications.

Ultrasound-Responsive Biomimetic Superhydrophobic Drug-Loaded Mesoporous Silica Nanoparticles for Treating Prostate Tumor.

Interfacial nanobubbles on a superhydrophobic surface can serve as ultrasound cavitation nuclei for continuously promoting sonodynamic therapy, but their poor dispersibility in blood has limited their biomedical application. In this study, we proposed ultrasound-responsive biomimetic superhydrophobic mesoporous silica nanoparticles, modified with red blood cell membrane and loaded with doxorubicin (DOX) (F-MSN-DOX@RBC), for RM-1 tumor sonodynamic therapy. Their mean size and zeta potentials were 232 ± 78.8 nm and -35.57 ± 0.74 mV, respectively. The F-MSN-DOX@RBC accumulation in a tumor was significantly higher than in the control group, and the spleen uptake of F-MSN-DOX@RBC was significantly reduced in comparison to that of the F-MSN-DOX group. Moreover, the cavitation caused by a single dose of F-MSN-DOX@RBC combined with multiple ultrasounds provided continuous sonodynamic therapy. The tumor inhibition rates in the experimental group were 71.5 8 ± 9.54%, which is significantly better than the control group. DHE and CD31 fluorescence staining was used to assess the reactive oxygen species (ROS) generated and the broken tumor vascular system induced by ultrasound. Finally, we can conclude that the combination of anti-vascular therapy, sonodynamic therapy by ROS, and chemotherapy promoted tumor treatment efficacy. The use of red blood cell membrane-modified superhydrophobic silica nanoparticles is a promising strategy in designing ultrasound-responsive nanoparticles to promote drug-release.

Non-fluorinated superhydrophobic film with high transparency for photovoltaic glass covers

Nowadays, there are several ways to prepare transparent superhydrophobic films for photovoltaic glass covers, but majority involve fluorosilane modifications, which are not only environmentally unfriendly but also can be hazardous to individuals. In this research, a non-fluorinated dip-coating method was proposed to prepare the film with a superhydrophobic layer and an antireflective layer. The antireflective layer with a network of nanopore-like structures was formed through a pore-forming agent. Then the superhydrophobic layer was deposited on above layer by simple immersion. Superhydrophobic silica nanoparticles would adhere to those structures, thus reducing the nanopore size and roughness, and increasing the transmittance. Finally, to enhance the films' self-cleaning abilities, a non-fluorinated silane modifier Hexamethyldisilazane (HMDS) was adopted. The film presented the average transmittance of 93.66 % in the wavelength range of 300 ∼ 1200 nm. The average static water contact angle (WCA) was 152°. In the self-cleaning test no dust was retained on the surface. The UV resistance test revealed that the film possessed outstanding UVA resistance. Moreover, the superhydrophobic films maintained transmittance stability against acidic (pH = 2) and deionized water (pH = 7) immersion. This environment friendly and low-cost preparation creates possibilities in photovoltaic glass covers and other fields.

Recyclable Superhydrophobic, Antimoisture-Activated Carbon Pellets for Air and Water Purification.

Activated carbon (AC) is a low-cost, highly porous material with large internal surface areas. It is highly efficient in absorbing moisture and a variety of chemical pollutants. Therefore, it has been widely used in air and water purification. However, the strong affinity to moisture often dominates, thus limiting AC's adsorption capacity of other pollutants in a humid environment and reducing its overall lifetime. In the study, superhydrophobic and anti-moisture AC (SA-AC) pellets are fabricated through one-step modification of commercially available AC with a solution consisting of superhydrophobic silica nanoparticles. The SA-AC pellets exhibit excellent water repellency with a static water contact angle reaching 160.3°. More importantly, they are moisture-resistant and air-permeable. Therefore, they preferably adsorb organic gases at humid conditions. The absorbed organic vapor can be released when they are transferred back to the dry atmosphere, for example, releasing approximately 35% of absorbed ethanol. The recoverability significantly reduces energy requirement compared to calcination or conventional extraction. Great adsorption capacity of organic dyes such as methylene blue, removal of oil-in-water microemulsions, and recyclability of SA-AC pellets are demonstrated. The morphology of the microporous structures of the SA-AC pellets is characterized against processing conditions, surface functional groups, and hierarchical structures tailored by the deposition of low-surface energy silica nanoparticles. The resulting micro-/sub-micropores on the pellet surface promote droplet condensation, thus displaying greater damp-proof performance than those treated by traditional modification. The study here presents a promising alternative for the efficient purification on large-scale air/water treatment.

Novel Janus composite hollow fiber membrane-based direct contact membrane distillation (DCMD) process for produced water desalination

In this study, an innovative Janus composite hollow fiber membrane-based direct contact membrane distillation (DCMD) process was boosted for desalination of actual produced water with elevated total dissolved solids (TDS) of 154,220 mg/L. The Janus composite hollow fiber membrane (Janus-HFM) was characterized with a thin and hydrophobic polyvinylidene difluoride (PVDF) and superhydrophobic silica nanoparticles (Si-R) outer layer, and a thick porous and hydrophilic PVDF and polyethylene glycol (PEG) inner layer. Compared to the neat PVDF hollow fiber membrane, the Janus-HFM showed both increased permeate water flux and improved energy efficiency with more than 99.99% salt rejection. The long-term desalination performance of the Janus-HFM was investigated via 200 h of continuous DCMD experiment. The results showed that the permeate water flux declined from 25.41 kg/m2h to 15.21 kg/m2h, and the salt rejection was 98.4% at the end of the operation. It was found that both scales and dissolved organic matters induced foulants accumulated at the feed side of the membrane due to the complex composition of the produced water. Nonetheless, the desalination performance decline can be effectively inhibited from 40% to 9.7% with a simple physical cleaning process by using the permeate water that recovered in the DCMD process.

Multifunctional Silica-Silicone Nanocomposite with Regenerative Superhydrophobic Capabilities.

Superhydrophobic surfaces have been garnering increased interest because of their adaptive characteristics. However, concerns regarding their durability and complex fabrication techniques have limited their widespread adoption. In our study, we have developed an effective, durable, and versatile silica-silicone nanocomposite that can be applied through spray coating or bulk synthesized as superhydrophobic monoliths through a facile, economic, and scalable fabrication technique. For spray-coated samples, superhydrophobicity was achieved for concentrations above 9%. However, poor adhesion was observed for concentrations above 20%. Through extensive surface morphology studies, it was determined that a delicate balance between the polymer and dispersed superhydrophobic silica nanoparticles exists at a concentration of 14%. This concentration is necessary for developing the desired hierarchical structure and providing sufficient adhesion with the substrate. The monoliths were fabricated into complex geometries, with superhydrophobicity being observed in the 5 and 9% specimens. The hierarchical structure was formed through controlled surface abrasion, which created the microscale roughness and concurrently exposed the embedded silica nanoparticles. It was found that a monolith with a concentration of 9% provides excellent water repellency as well as a suitable emulsion viscosity to facilitate the molding process. Though compressive loading (up to 10 MPa) damages the monolith, the superhydrophobic performance can be quickly restored through abrasive layer removal. Both spray-coated and monolith specimens retained their superhydrophobicity after being subjected to high temperatures (up to 350 °C) and corrosive environments (pH 1-13) for 2 h.

Hydrophobic Silica with Potential for Water-Injection Augmentation of a Low-Permeability Reservoir: Drag Reduction and Self-Cleaning Ability in Relation to Interfacial Interactions.

An aqueous nanofluid containing superhydrophobic silica nanoparticles with a high surface activity and an average size of 7 nm was used to enhance the water injection of a low-permeability well. The mechanism for the aqueous nanofluid to enhance water injection was discussed. Findings indicate that the silica aqueous nanofluid can greatly increase the effective water permeability even after injecting water for 2100 pore volumes. This is because the hydrophobic silica nanoparticles can be well adsorbed onto the surface of the porous channels to cause hydrophilic to hydrophobic transformation. Both the hydrophobic capillary force and adhesion work contribute to increasing water injection; and in particular, there is a critical point in the pressure-permeability curves for the rock cores with different wettabilities. Only above the critical point, the hydrophobic rock core exhibits a higher effective water permeability than that of the hydrophilic one, which is imperative for drag reduction. Moreover, the hydrophobic rock core surface has a remarkable self-cleaning ability and can reduce the expansion ratio of clay and inhibit the formation of scale in association with the increase of effective porosity via decreasing the hydration film amount. This approach, highlighting the important role of wettability alteration in increasing water injection, could potentially promote the application of a silica aqueous nanofluid in enhanced oil recovery.

Coating Sand with New Hydrophobic and Superhydrophobic Silica/Paraffin Wax Nanocapsules for Desert Water Storage and Transportation

Paraffin wax emulsions have gained immense attention as a cheap, environment-friendly, and aroma-free material for preparing superhydrophobic coatings. In this work, paraffin wax (PWs) capsules consisting of hydrophobic silica nanoparticles were used for coating desert sand. Different types of the hydrophobic silica nanoparticles, modified with new oleylamino- and oleylamide silane precursors, were prepared in the presence and absence of paraffin waxes. The particle sizes, surface charges, thermal stability, surface morphologies, and wetting characteristics of these nanoparticles were investigated. The combination of these superhydrophobic silica nanoparticles and desert sand, showed excellent water repellency; stable water droplets remained on the sand surface, without any wetting or permeation. Furthermore, the mixing of the superhydrophobic sand with untreated sand (mixing ratio 1:10 wt %), with a thickness of 2 cm, sustained a great water-holding capacity with a water column height of 35 cm. The good thermal stability of the PWs capsules containing hydrophobic silica nanoparticles, along with their good water-holding capacity, make them potential candidates for developing superhydrophobic sand for desert water storage and transportation.

Bio-based and photocrosslinked electrospun antibacterial nanofibrous membranes for air filtration

Air pollution is becoming more and more severe especially in developing countries. It is urgent to seek an effective protection for the unacceptable levels of the air pollution. Up to date, the air filtration is a widely used method to protect us from the air pollution. However, most of the air filtration membranes in fabrication process is required to use harmful organic solvents. Here, we report a human friendly, multifunctional and bio-based chitosan/poly (vinyl alcohol) air filtration membrane via green electrospinning and UV-cured. This green approach avoid use hazardous organic solvents which caused the residual solvents could bring the human subprime damage. Specifically, the superhydrophobic silica nanoparticles is introduced on the nanofibers to formation of the rough surface to increase filtration efficiency. In addition, the Ag nanoparticles (NPs) are fabricated on the surface through UV reduction of AgNO3 to achieve the aim of antibacterial treatment. The CS/PVA@SiO2/Ag NPs membranes not only possess excellent filtration performance but efficiently antibacterial activities. As this green, multifunctional and bio-based CS/PVA@SiO2/Ag NPs air filtration membranes have several superior features like high air filtration performance, biological compatibility and antibacterial, it has great potential application in eco-friendly air filtration materials, especially in personal air filtration materials.

Facile one step synthesis of stable suspended superhydrophobic silica nanoparticles in the aqueous solution by using of anionic surfactant

It is the first time that stable suspended superhyrophobic silica nanoparticles were synthesized in the aqueous solution with a facile, fast and non-polluting method by using of vinyl trimethoxy silane as precursor of silica particles by a simple sol gel process. Also the using of ammonium lauryl ether sulfate (an anionic surfactant) during synthesis leading to lower particle size, more stable suspended particle and higher contact angle of superhyrophobic silica that significantly improved by increasing of surfactant concentration. The results shown particle agglomeration and sedimentation arise by addition of H+ concentration due to decreasing of zeta potential.

Facile preparation of superhydrophobic silica nanoparticles by hydrothermal-assisted sol–gel process and effects of hydrothermal time on surface modification

Superhydrophobic silica nanoparticles were prepared by hydrothermal-assisted sol–gel process using a two-step synthesis route. Silica nanoparticles were obtained by hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Hexadecyltrimethoxysilane (HDTMS) was added to allow the condensation reaction between HDTMS hydroxyl group and silica hydroxyl group, rendering silica particles hydrophobic. Silica nanoparticles had a HDTMS/TEOS molar ratio of 2:40 and exhibited good hydrophobic property with a high water contact angle of 156.1°. Water droplet rolled off the surface of silica powder owing to a low sliding angle of 3.6°. When hydrothermal time of TEOS decreased from 120 to 60 min, all silica powders gave rise to high water contact angles (≥154.8°) and low sliding angles (≤5.5°). However, silica powder became hydrophilic when HDTMS and TEOS were added to the precursor together. This facile preparation of superhydrophobic silica nanoparticles with short reaction time provided the advantages for potential application in industrial production.

Water-based acrylate copolymer/silica hybrids for facile preparation of robust and durable superhydrophobic coatings

Resin based superhydrophobic coatings are effective to construct robust superhydrophobic surfaces on large scale without limitation of substrates. However, for most of the common resin based superhydrophobic coatings, it is inevitable to deteriorate environmental or health problems due to release of a large amount volatile solvents. In this work, a kind of water-based organic/inorganic hybrid consisted of acrylate copolymers and superhydrophobic silica nanoparticles were synthesized. The highly water-repellent silica nanoparticles were successfully involved into the aqueous dispersion of acrylate copolymers without additional surfactants. The as-synthesized hybrids simultaneously retain the excellent film-forming property of acrylate resins and amplify the contributions of low surface energy nanoparticles to the superhydrophobicity. Robust superhydrophobic coatings (CA > 160°, CA < 7°) with high adhesion strength, good scratch-resistance and excellent abrasion-resistance were constructed using the synthesized hybrids with significantly reduced content of low surface energy particles and organic solvent. The hybrid coating can stand abrasion up to 300 cycles with a fine sand paper and up to 1200 cycles under rough sand paper abrasion. Benefited from its good water-repellence property, the hybrid coating with a water-based formula not only showed improved water-resistance in comparison with commercial products; but also displayed attractive performances in self-cleaning and oil/water separation processes.

Environmental response nanosilica for reducing the pressure of water injection in ultra-low permeability reservoirs

The super-hydrophobic silica nanoparticles are applied to alter the wettability of rock surface from water-wet to oil-wet. The aim of this is to reduce injection pressure so as to enhance water injection efficiency in low permeability reservoirs. Therefore, a new type of environmentally responsive nanosilica (denote as ERS) is modified with organic compound containing hydrophobic groups and “pinning” groups by covalent bond and then covered with a layer of hydrophilic organic compound by chemical adsorption to achieve excellent water dispersibility. Resultant ERS is homogeneously dispersed in water with a size of about 4–8 nm like a micro-emulsion system and can be easily injected into the macro or nano channels of ultra-low permeability reservoirs. The hydrophobic nanosilica core can be released from the aqueous delivery system owing to its strong dependence on the environmental variation from normal condition to injection wells (such as pH and salinity). Then the exposed silica nanoparticles form a thin layer on the surface of narrow pore throat, leading to the wettability from water-wet to oil-wet. More importantly, the two rock cores with different permeability were surface treated with ERS dispersion with a concentration of 2 g/L, exhibit great reduce of water injection pressure by 57.4 and 39.6%, respectively, which shows great potential for exploitation of crude oil from ultra-low permeability reservoirs during water flooding.

Octadecyl‐silica—PVDF membrane of superior MD desalination performance

ABSTRACTDespite its widespread industrial and residential uses for production of potable water, the reverse osmosis (RO) desalination process has some drawbacks by discharging harmful concentrated saline water as reject stream. A hydrophobic porous membrane can treat such environmentally unfriendly RO reject stream via Membrane Distillation (MD) process. Here, we describe preparation of superior polyvinylidenefluoride (PVDF) membrane modified with superhydrophobic silica nanoparticles for desalination application. Superhydrophobicity (contact angle of 151°) of silica nanoparticles of 7 nm sizes was achieved by reaction of the silica particles with octadecyltrichlorosilane in toluene to form SiOSi links with C18 alkyl chain. A homogeneous polymer dope mixture containing a desired amount of modified silica colloids suspended in toluene was used for the membrane preparation. The PVDF membrane with optimal silica content exhibited excellent flux with &gt;99% salt rejection efficiency when used for MD at room temperature from the saline water feed of 3.5 wt % NaCl. The prepared hydrophobic PVDF membrane has the potential for MD application in treating the RO reject stream and other aqueous industrial effluents. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46043.

Green electrospun and crosslinked poly(vinyl alcohol)/poly(acrylic acid) composite membranes for antibacterial effective air filtration

Air pollution has become a major environmental concern given the ever increasing levels of particulate matter (PM) and the increased in treatment-resistant bacterial and viral strains. Major efforts are therefore required into the development of air filtration and purification technology as well as novel, alternative antiviral and antibacterial treatment modalities. Here, we report an environmentally friendly method for the generation of multifunctional poly(vinyl alcohol)/poly(acrylic acid) (PVA-PAA) composite membranes via green electrospinning and thermal crosslinking. Superhydrophobic silica nanoparticles were then incorporated into the fibers resulting in a rough surface, after which AgNO3 was introduced, resulting in the formation of Ag nanoparticles through UV reduction. The PVA-PAA-SiO2-Ag NPs membranes were found to possess high air filtration performance (with >98% filtration efficiency for PM2.5) as well as potent antibacterial and antiviral activities. The green synthesis approach avoids the use of hazardous organic solvents, thereby bypassing any potential toxicity concerns caused by organic solvent residues. These newly designed PVA-PAA-SiO2 NPs-Ag NPs nanofibrous membranes with many superior features (e.g. high filtration efficiency, high tensile strength, biological compatibility, and antibacterial properties) can be applied in eco-friendly air filtration materials, in particular for personal air filtration devices.

Superhydrophobic silica nanoparticles as ultrasound contrast agents

Microbubbles have been widely studied as ultrasound contrast agents for diagnosis and as drug/gene carriers for therapy. However, their size and stability (lifetime of 5–12min) limited their applications. The development of stable nanoscale ultrasound contrast agents would therefore benefit both. Generating bubbles persistently in situ would be one of the promising solutions to the problem of short lifetime. We hypothesized that bubbles could be generated in situ by providing stable air nuclei since it has been found that the interfacial nanobubbles on a hydrophobic surface have a much longer lifetime (orders of days). Mesoporous silica nanoparticles (MSNs) with large surface areas and different levels of hydrophobicity were prepared to test our hypothesis. It is clear that the superhydrophobic and porous nanoparticles exhibited a significant and strong contrast intensity compared with other nanoparticles. The bubbles generated from superhydrophobic nanoparticles sustained for at least 30min at a MI of 1.0, while lipid microbubble lasted for about 5min at the same settings. In summary MSNs have been transformed into reliable bubble precursors by making simple superhydrophobic modification, and made into a promising contrast agent with the potentials to serve as theranostic agents that are sensitive to ultrasound stimulation.

Fabrication of Superhydrophobic Silica Nanoparticles and Nanocomposite Coating on Glass Surfaces

Fabrication of Superhydrophobic Silica Nanoparticles and Nanocomposite Coating on Glass Surfaces