Hydrophobic Silica Research Articles

Superhydrophobic Nanocomposite Coatings of Hydrophobic Silica NPs and Poly(methyl methacrylate) with Notable Self‐Cleaning Ability

AbstractThe present paper describes a facile and inexpensive dip coating method for preparation of hierarchical superhydrophobic nanocomposite coating. The hydrophobic silica nanoparticles (NPs) are synthesized via sol–gel technique. The superhydrophobicity of the coating is controlled by adjusting the concentration of silica NPs in poly (methyl methacrylate) (PMMA). After optimization, the coating exhibited water contact angle of 165° and sliding angle of 4°. The surface morphology of the superhydrophobic coatings revealed hierarchical rough structure formed on the glass substrate, which enable air trapping. The prepared superhydrophobic coating showed wetting stability under water jet impact with notable self‐cleaning performance. The mechanical stability of the superhydrophobic coating is studied using sandpaper abrasion and adhesive tape peeling test. Such highly non‐wettable and self‐cleaning coatings have potential in various practical applications.

Superhydrophobic PU Sponge Modified by Hydrophobic Silica NPs—Polystyrene Nanocomposite for Oil–Water Separation

AbstractIn this study, the hydrophobic silica nanoparticles (NPs) are synthesized by simple sol–gel processing of polymethylhydrosiloxane (PMHS). The nanocomposite solution is prepared by adding hydrophobic silica NPs in polystyrene solution and applied on the skeleton of polyurethane sponge by simple immersion‐drying process. The as‐prepared sponges exhibited superhydrophobic property with water contact angle 161° and oil contact angle nearly 0° and can separate oil from oil–water and oil–muddy water mixture. The superhydrophobic sponge has sustainable anti‐wetting property under cross sectional cutting, pressing and twisting, and different pH environment. Such superhydrophobic sponge is suitable for practical application on a large scale.

Superhydrophobic PVC/SiO2 Coating for Self‐Cleaning Application

AbstractA lotus leaf like self‐cleaning superhydrophobic coating has high demand in industrial applications. Such coatings are prepared by alternative dip and spray deposition techniques. A layer of polyvinyl chloride is applied on glass substrate by dip coating and then spray coated a suspension of hydrophobic silica nanoparticles at substrate temperature of 50 °C. This coating procedure is repeated for three times to achieve rough surface morphology which exhibits a water contact angle of 169 ± 2° and sliding angle of 6°. The superhydrophobic state of the coating is still preserved when water volume of 1.2 L is used to impact the water drops on coating surface. The stability of the wetting state of the coating is analyzed against the water jet, adhesive tape and sandpaper abrasion tests. The prepared superhydrophobic coating strongly repelled the muddy water suggesting its importance in self‐cleaning applications.

Synthesis and characterization of highly hydrophobic, oil-absorbing aerogels for oil spill applications; A Review

The review report reflects on the potential of highly hydrophobic silica aerogel as a viable material for oil absorption application in the clean-up of oil spills on oceans. The review presents the conventional clean-up technologies, silica aerogel synthesis and coatings by sol-gel method and simulation techniques to predict the maximization of efficiency as well as mechanical characteristics for practical applications.

Kinetic and thermodynamic study of CO2 storage in reversible gellan gum supported dry water clathrates

The effects of "Dry Gel" on the carbon dioxide hydrate formation and storage capacity were studied. Gel-supported dry water (Dry Gel) was prepared by mixing gelling agents, hydrophobic silica nanoparticles, water, and air in a high-speed blender. The kinetic parameters of carbon dioxide hydrate formation such as mole of consumed gas, induction time, gas uptake rate, storage capacity, final conversion of water to hydrate, and apparent rate constant were investigated in the presence of dry gel with different gel strength (0 to 15 wt.%) at two silica ratios (5 and 10 wt.%). The experiments of hydrate formation were performed using a 200 cc stainless-steel vessel with and without stirring under the initial condition of 21 bars and 15 °C. Meanwhile, the thermodynamic recyclability of both dry water and dry gels over multiple hydrate cycles were studied. Besides, we utilized the diffusion-reaction kinetics model of Englezos and Bishnoi for calculating the apparent rate constant of hydrate growth. The van der Waals-platteeuw model, through a reversed micelle approach, was used to obtain hydrate phase equilibrium conditions. Results revealed that the amount of gas uptake increased significantly in both dry water and dry gel systems compared to pure water. It was found that dry gel with 15 wt.% gellan gum could substantially improve the storage and recyclability of CO2 hydrate by decreasing the decay percent from 68.8 to 5.1 over repeating seven hydrate cycles.Moreover, the more Nano-silica content, the better the storage repeatability was observed. It was also shown that the equilibrium hydrate formation conditions were approximately stable in the presence of dry gels. Mixing seemed to be critical for multiple freezing-thawing hydrate cycles since it could reduce the reaction and induction time significantly. Finally, the dry water and dry gel can be used as a promising platform for carbon dioxide capturing using clathrate through the recyclability of hydrate formation.

Slip length measurement of pdms/hydrophobic silica superhydrophobic coating for drag reduction application

This paper aims to study the drag reduction of a superhydrophobic nanocomposite coating for engineering applications. In the method developed, a suspension of hydrophobic silica nanoparticles in PDMS/toluene solution was prepared. Then a spray-deposition method is used to deposit a layer of nanocomposite composed of PDMS/hydrophobic silica nanoparticles on the surface. After curing the samples at 100 °C for 1 h the nanocomposite coating was prepared. The surface morphology of the coating was characterized by scanning electron microscopy and static water contact angle measurement. The superhydrophobic properties of fabricated surfaces are investigated through different PDMS/hydrophobic silica nanoparticles ratios. It was found that the presented nanocomposite coating method was an effective technology which was suitable to form large-area superhydrophobic coating with a water droplet (5 μL) roll-off angle of less than 5°. The hydrostatic pressure test showed that the Cassie−Baxter state of the fabricated coating is stable in front of the applied pressure up to 50 kPa. Drag reduction tests showed that the air-layer placed at the water-superhydrophobic interface was stable in front of wall shear stress up to 11 Pa. The maximum drag reduction and slip length were measured about 25% and 70 μm, respectively.

Effect of the ratio between hydrophobic mesoporous silica (Aerosil®R812S) and water on the formation and physical stability of water-entrapped self-assembly particle

Potential effect of the proportionality between Aerosil®R812S over the water on the formation of water entrapped self-assembly core-shell structure is the main aim of this studies. Self-assembly hydrophobic silica particle (SAHS) containing water was fabricated by abruptly incorporation of water into R812S. Five different weight percent of R812S were investigated in terms of the ability to form SAHS including their physical stability. The lowest ratio of 1% was not able to form SAHS. More than 2 up to 5% of R812S yielded core-shell structure of SAHS in the dry solid form. The smaller size of SAHS would be the result of higher level of R812S used. The finer the water droplet the more consume the silica particle used in order to gain stable SAHS. In terms of stability, they disclosed unacceptable qualities at 6 months of storage due to either remarkable phase separation or squeezing out of inner water core. It should be due to the thermodynamic driven forces that accelerated the movement of both water and silica shell to coalesce. In conclusion, the stable SAHS comprised of sufficient amount of R812S (more than 2% by weight) with water. It could be kept within short term period with acceptable properties.

Fabrication of Carbon-Like, π-Conjugated Organic Layer on a Nano-Porous Silica Surface.

This paper presents a new type of black organic material-porous silica composite providing an extremely highly selective adsorption surface. This black composite was prepared by lamination on nano-sized pores with a carbon-like, π-extended structure, which can be converted via the on-site polymerization of 1,5-dihydroxynaphthalene with a triazinane derivative and a thermally induced condensation reaction with denitrification. This bottom-up fabrication method on porous materials had the great advantage of maintaining the pore characteristics of a raw porous material, but also the resultant black surface exhibited an extremely high molecular-shape selectivity; for example, that for trans- and cis-stilbenes reached 14.0 with the black layer-laminated porous silica, whereas it was below 1.2 with simple hydrophobized silica.

UV-NIR Dual-Responsive Nanocomposite Coatings with Healable, Superhydrophobic, and Contaminant-Resistant Properties.

Self-healing superhydrophobic coatings are attracting interest, but it still remains a great challenge to develop facile and fast self-healing strategies for superhydrophobic coatings. In this work, a novel environmentally friendly self-healing superhydrophobic coating based on an ultraviolet (UV)/near-infrared light (NIR) dual-responsive action was fabricated by blending UV-responsive microcapsules with NIR-responsive carbon nanoparticles (NPs), hydrophobic silica NPs, and waterborne silicone latex. The UV-responsive microcapsules were simply prepared through the electrostatic adsorption of negatively charged TiO2 NPs onto a positively charged microcapsule surface. The UV-NIR dual-responsive properties were mainly reflected in the healing of the superhydrophobic property for coatings through NIR or UV light irradiation. The self-healing process could be repeated many times, which can be attributed to the continued release of fluorine silane (FAS-13) loaded in the UV-responsive microcapsules to the coating surface. The combinations of NIR and UV responses endow the coating with the characteristics of fast healing and large-area healing when damaged by the external environment. In addition, the self-healing superhydrophobic coating film has excellent oil, corrosion, and wear resistance, satisfying the requirements for realistic outdoor applications.

Influence of surface wettability on methane hydrate formation in hydrophilic and hydrophobic mesoporous silicas

The methane hydrate (MH) formation process in confinement was investigated using high-pressure methane sorption experiments on two wet materials with similar pore size distributions, B – PMO (hydrophobic) and MCM – 41 (hydrophilic). Their methane sorption isotherms possess two discrete methane gas consumption steps at ~10 bar and ~ 30 bar at 243 K. A systematic analysis reveals that external water and the so-called ‘core water’ inside the pore is rapidly consumed in the first step to form bulk-like hydrate, whereas adsorbed water is slowly consumed in the second step to form less stable confined hydrates at higher pressures. Synchrotron powder X-Ray results confirm methane hydrate structure I and reveal that bulk ice is swiftly and fully converted to hydrate in MCM – 41, whereas inactive bulk ice co-exists with MH in B – PMO at 6 MPa demonstrating the huge impact of the surface wettability on the water’s behavior during MH formation.

Comparisonal studies of surface modification reaction using various silylating agents for silica aerogel

Surface modification is one of the important steps for synthesizing hydrophobic silica aerogels by ambient pressure drying in which silylating agent plays a vital role. Trimethylchlorosilane and many kinds of methoxysilanes like trimethylmethoxysilane, dimethyldimethoxysilane, and methyltrimethoxysilane have been used as the silylating agents. In this work, silylation effects were investigated with different molar ratios of silylating agent/n-hexane mixture. In addition, the mechanism of the silylation reaction is explained based on the molecular structures by considering the number of methoxy/methyl groups. The silylation extent was characterized by using optical imaging, bulk density and porosity analyses, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, and contact angle measurements. It has been found that the methoxysilane-based silylating agents can be used as a replacement without producing the harmful hydrochloric acid and retaining the similar tendency to trimethylchlorosilane in surface modification. This research approach seeks to an alternative silylating agent by investigating the impact on the surface modification based on the molecular structural parameters and reaction mechanisms.

Preparation of Continuous Highly Hydrophobic Pure Silica ITQ-29 Zeolite Layers on Alumina Supports.

The preparation of continuous layers of highly hydrophobic pure silica ITQ-29 zeolite, potentially applicable as hydrophobic membranes for separation of molecules based on their polarity, has been investigated. Continuous layers of intergrown ITQ-29 zeolite crystals were successfully grown on porous alumina supports by optimization of the synthesis conditions, such as the appropriate selection of the seeds, the procedure for the gel preparation, and the calcination conditions. This resulted in the formation of all silica ITQ-29 zeolite layers without the presence of germanium required in previously reported ITQ-29 membranes, with the subsequent improvement in quality and stability, as verified by the absence of cracks after calcination. We have proved that the incorporation of aluminum from the support into the zeolite layer does not occur, neither during the secondary growth nor through migration of aluminum species during calcination.

Evaluation of microstructure, thermal, and mechanical properties of the green lignin‐based polyurethane/hydrophobic silica nanocomposite foam

AbstractIn the present study, lignin‐based polyurethane foam (LPUF) and hydrophobic silica LPUF (SLPUF) were synthesized using different concentrations of silica nanoparticles (SNP). The effect of SNP on the structure and properties of SLPUF samples was investigated and compared with LPUF through the scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), and compressive tests. The FT‐IR results showed changes in the H bonding interactions between the structures of SLPUF samples. Moreover, the SEM results indicated a decrease in the cell size of SLPUF samples. Incorporation of SNP improved the thermal stability of SLPUF samples while the compressive strength of SLPUF samples decreased in comparison with LPUF. Furthermore, the DMTA results revealed a decrease in the glass transition temperature from 90°C (LPUF) to around 52°C (SLPUF samples). This means that applying the hydrophobic SNP changes the foam type from a rigid foam to soft one. Therefore, significant changes were observed in the physical–chemical properties of the SLPUF samples compared to the LPUF.

Preparation of PDLLA based nanocomposites with modified silica by in situ polymerization: Study of molecular, morphological, and mechanical properties

In order to prepare poly-D,L-lactide/silica nanocomposites and to improve the interfacial adhesion between these two materials, silanization of silica was realized adopting two different organosilanes, i.e. 3-glycidyloxytrimethoxysilane or 3-aminopropyltrimethoxysilane. Then, resulting modified silica with epoxy or amino terminal functions served as initiating sites for D,L-lactide in situ polymerization allowing the production of poly-D,L-lactide/silica nanocomposites.Silica dispersion and mechanical properties of these hybrids were compared to composites prepared with hydrophilic or hydrophobic commercial silica by in situ polymerization. These latter composites disclosed heterogeneities with microscale agglomerates and a drop in mechanical properties for 5 wt% of silica loading. In contrast, composites made from poly-D,L-lactide chains chemically grafted on silica carrying initiation sites disclosed nanoscale dispersion of nanofiller in the PDLLA matrix. In particular, with only 1 wt% of these modified silicas, thanks to the nanoscale dispersion of the inorganic nanofiller, an improvement of 24 % for Young modulus and 51 % for ultimate tensile strength was achieved.

Synthesis of PMHS–PDMS composite membranes embedded with silica nanoparticles and their application to separate of DMSO from aqueous solutions

The study focused on the performance enhancement of a PDMS membrane using PMHS as the curing agent, and by incorporation of silica nanoparticles with four different silica contents of 2.5, 5, 7.5 and 10 wt%. The membranes were synthesized and applied as the separation elements to improve the separation of DMSO from their aqueous solutions. The properties of the membranes were studied by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), field emission scanning electronic microscopy and thermal gravimetric analysis (TGA). ATR-FTIR results indicated the integration of silica nanoparticles into the nanocomposite membranes and also confirmed the cross-linking reaction between the PMHS and the PDMS. The TGA curve of hybrid membranes displayed that the proper incorporation of SiO2 nanoparticles could clearly improve the thermal stability of the unfilled membrane. Moreover, swelling of prepared membranes was attained for different feed solutions. Results showed that the separation factor and flux of the PDMS/PMHS membrane were enhanced by the incorporation of hydrophobic silica particles into the composite. The maximum separation factor of 830.33 was achieved for the feed mixture with an initial DMSO concentration of 25 vol%, using the membrane with 5 wt% silica content.

Hydrophobic silica aerogels synthesized in ambient conditions by preserving the pore structure via two-step silylation

Surface modification, which is simply about the end-capping of the reactive silanol groups located in silica wet gel to satisfy hydrophobic behavior, has great importance in the production of silica aerogels in ambient conditions. In this study, silica aerogels were synthesized with a sol-gel method via ambient pressure drying. A two-step surface modification was performed on wet gels by using various silanes with different contents (6%, 10% or 20% by vol in n-hexane) to control the extent of irreversible shrinkage during drying. Mono-functional (TMCS) and three-functional silanes (MTMS, MTES and MEMO) were selected for this purpose. The impact of the type and amount of the silylating agents on the microstructure, pore characteristics and hygroscopic nature of resulting aerogels were identified by conducting FTIR, SEM and BET analyses and contact angle measurements. According to characterization results, MTES exhibits a competitive performance compared to classically used TMCS, as the silica aerogels modified with 10% of MTES was obtained in a well-developed with mesoporous structure with very high specific surface area (SBET = 964m2/g) and high hydrophobicity (Θ = 137°). On the other hand, organically functionalized silane MEMO and MTMS, also display noteworthy results (monolithical structure with highly developed porous network and high degree of hydrophobicity) at the low contents (at 6% and 10%). These outcomes are crucial as they may encourage the future attempts on introducing three-functional silanes during surface modification, as these silanes yield high silylation performance and causes the synthesis of well-qualified silica aerogel in ambient conditions.

Facile synthesis of nano silica-based coating on API5L-x80 steel to achieve ultra non-wetting surface and its corrosion resistance

A facile and acceptable way for arrangement of non-wetting ultra-hydrophobic silica coatings is proposed in this work. The X80 steel samples with the dimension of 10 × 10 × 2 mm were used as the base metal. Commercially silica nanoparticles were modified using alkoxide organosilane as an active modifying agent. The ultra-hydrophobic silica coatings with a water contact angle of 142° were achieved (ultra-high degree of contact angle). The prepared silica coatings exhibit ultra-hydrophobicity and excellent corrosion behaviors under 3.5 wt% NaCl immersion testing conditions, which surfaces with 2.0% and 2.5% of hydrophobic silica specimens show a low corrosion potential and current, significantly. The corrosion resistance of the samples was evaluated by the electrochemical impedance spectroscopy technique also the microstructure, and surface topography of the samples was evaluated with scanning electron microscopy and Fourier transform infrared, respectively. This coating method is expected such a convincing process technology against fabricating self-cleaning coatings for the encouraging industrial implementation.

Designing a Support for Lipase Immobilization Based On Magnetic, Hydrophobic, and Mesoporous Silica.

A mesoporous, magnetic, and hydrophobic material was designed step by step to act as a support for lipase immobilization. Its pore size (8.0 nm) is compatible with the size of lipase from Thermomyces lanuginosus (TLL), and its hydrophobic surface (contact angle of a water drop = 125°) was planned to interact with lipase on its interfacially activated form (open conformation). The presence of magnetite particles provides magnetic retrieval of the material and enables recyclability of the biocatalysts. Regarding immobilization parameters, the hydrophobic support was tested in comparison to the unmodified hydrophilic support in phosphate buffer solution (50 mmol L-1, pH 7.5) at 25 °C. Hydrophobicity was found to be critical for the amount of immobilized TLL (immobilization yield of 97% versus 36% for the hydrophilic support), whereas the hydrophilic support favors the native conformational state and substrate access to the enzyme's catalytic site (specific activity of 5.7 versus 4.7 U g-1 for the hydrophobic support, even when it has higher TLL content). Therefore, the hydrophobic support immobilizes higher amounts of TLL and the hydrophilic support keeps the enzyme hyperactivated. Last, due to the stronger interactions of TLL with hydrophobic surfaces, the hydrophobic support offers better preservation of enzyme activity in repeated cycles (76% of activity retained after three cycles versus 50% for the hydrophilic support).

The Effect of Dissolved Gases on the Short-Range Attractive Force between Hydrophobic Surfaces in the Absence of Nanobubble Bridging.

The short-range attractive forces between hydrophobic surfaces are key factors in a wide range of areas such as protein folding, lipid self-assembly, and particle-bubble interaction such as in industrial flotation. Little is certain about the effect of dissolved (well-controlled) gases on the interaction forces, in particular in those systems where the formation of surface nanobubble bridges is suppressed. Here, we probe the short-range attractive force between hydrophobized silica surfaces in aqueous solutions with varying but well-controlled isotherms of gas solubility. The first contact approach force measurement method using AFM shows that decreasing gas solubility results in a decrease of the force magnitude as well as shortening of its range. The behavior was found to be consistent across all four aqueous systems and gas solubilities tested. Using numerical computations, we corroborate that attractive force can be adequately explained by a multilayer dispersion force model, which accounts for an interfacial gas enrichment (IGE), that results in the formation of a dense gas layer (DGL) adjacent to the hydrophobic surface. We found that the DGL on the hydrophobic surface is affected only by the concentration of dissolved gases and is independent of the salt type, used to control the gas solubility, which excludes the effect of electrical double-layer interactions on the hydrophobic force.

Removal of copper ions using poly (acrylic acid-co-acrylamide) hydrogel microspheres with controllable size prepared by W/O Pickering emulsions

Poly (acrylic acid-co-acrylamide) hydrogel microspheres were prepared via Pickering emulsion polymerization with hydrophobic silica as emulsifiers. The functional groups and the morphology of the hydrogel microspheres were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The effect of the dosage of hydrophobic silica on Pickering emulsion polymerization was investigated, and the hydrogel microspheres with different particle sizes were used to remove copper ions in water. The results showed that the diameter (D) of the hydrogel microspheres was inversely proportional to the dosage (S) of the hydrophobic silica used. The size of the hydrogel microspheres mainly affected the adsorption equilibrium time, and the maximum adsorption capacity could reach 85 mg/g at pH = 5. The results of desorption experiment demonstrated that copper ions were adsorbed by hydrogel microspheres mainly through chemical interaction. Pickering emulsion polymerization was an efficient and environmentally friendly approach for the fabrication of granular hydrogels.