Superhydrophobic Silica Research Articles

Building a mechanically stable polydimethylsiloxane/silica superhydrophobic coating on poly(chloro-p-xylylene) film by introducing a polydimethylsiloxane adhesive layer

Building a superhydrophobic coating on polymer films is an important way to obtain water-proof surfaces. However, due to the poor mechanical strength and weak adhesion between coating and substrate, the superhydrophobicity of the coating is easily lost under mechanical loads. In this study, a facile approach was proposed to build a mechanically stable superhydrophobic poly(chloro-p-xylylene) (PPXC) film by pre-coating a polydimethylsiloxane adhesive layer (PDMS AL) on the original PPXC film and coating a superhydrophobic PDMS and silica (PDMS/SiO2) layer on the PDMS AL layer. As demonstrated by Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) measurements, the thermal cross-linking reaction between the PDMS/SiO2 coating and the PDMS AL layer could dramatically promote the interaction between the PDMS/SiO2 coating and the PPXC film. By tuning pre-curing time and the content of PDMS AL, the mechanical stability of the PDMS/SiO2 coating on PPXC film could be adjusted. Under the optimal conditions of pre-curing time and the content of PDMS AL, the PPXC film showed robust superhydrophobicity and self-cleaning ability against various mechanical damages, such as 3M tape peeling and cyclic abrasion. The superhydrophobic coating on PPXC film with PDMS AL showed a higher peeling resistance than that on PPXC film without PDMS AL. Moreover, the superhydrophobic coating on PPXC film with PDMS AL maintained its original superhydrophobicity even after 4000 cycles of abrasion.

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.

Interfacing superhydrophobic silica nanoparticle films with graphene and thermoplastic polyurethane for wear/abrasion resistance

HypothesisNanoparticle films are one of the most suitable platforms for obtaining sub-micrometer and nanometer dual-scale surface texture required for liquid repellency. The assembly of superhydrophobic nanoparticles into conformal and strongly adherent films having abrasion-induced wear resistance still poses a significant challenge. Various techniques have been developed over the years to render nanoparticle films with good liquid repellent properties and transparency. However, forming abrasion resistant superhydrophobic nanoparticle films on hard surfaces is challenging. One possibility is to partially embed or weld nanoparticles in thin thermoplastic primers applied over metals. ExperimentsHexamethyldisilazane-functionalized fumed silica nanoparticle films spray deposited on aluminum surfaces were rendered abrasion resistant by thermally welding them into thermoplastic polyurethane (TPU) primer applied a priori over aluminum. Different solvents, nanoparticle concentrations and annealing temperatures were studied to optimize nanoparticle film morphology and hydrophobicity. FindingsThermal annealing at 150 °C enhanced stability and wear resistance of nanoparticle films. A thin thermal interface layer of graphene nanoplatelets (GnPs) between the primer and the nanoparticle film significantly improved superhydrophobic wear resistance after annealing. As such, superhydrophobic nanocomposite films with the GnPs thermal interface layer displayed superior abrasion-induced wear resistance under 20 kPa compared to films having no GnPs-based thermal interface.

Superhydrophobic oligoaniline-containing electroactive silica coating as pre-process coating for corrosion protection of carbon steel

This paper provided a novel coating system for Q235 steel using electrodeposited oligoaniline modified silica coating (E-M-SiO2) as a pre-process coating, which was prepared by one step coelectrodeposition of a mixture of tetraethyl orthosilicate (TEOS) and N,N′-Bis(4′-(3-triethoxysilylpropylureido)-phenyl)-1,4-quinonenediimine (TSUPQD). Microstructure, contact angle, electroactivity and anticorrosion performance were investigated by FTIR, UV–vis, AFM, SEM, OCA20 contact angle analyzer, CV and CHI-660E electrochemical workstation. The CA test indicated, in comparison with pure silica and sol–gel modified silica hybrid coatings, the electrodeposited modified silica coating exhibited a super hydrophobic performance. The CV test illustrated that the special redox property of aniline trimer was maintained in these modified silica hybrid coatings. More importantly, the anticorrosion effectiveness for Q235 steel in 3.5% NaCl solution was improved by the addition of oligoaniline modified silica as the pre-process coating. By comparison, it turned out that the epoxy/E-M-SiO2 coating system presented the lowest icorr value and the highest |Z|0.01Hz value. The corrosion protection mechanism was the synergistic effect of super hydrophobic nature of E-M-SiO2 pre-process coating and special catalytic capability of aniline trimer unit, which effectively restrained the permeation of corrosion medium and induced the formation of passive films consisted of α-Fe2O3 and Fe3O4 on the Q235 surface.

A superhydrophobic mesostructured silica as a chiral organometallic immobilization platform for heterogeneous asymmetric catalysis

Super-hydrophobic and mesostructured silica-supported molecular catalysts were developed and their applications in enantioselective organic transformation were investigated.

Magnetically driven superhydrophobic silica sponge decorated with hierarchical cobalt nanoparticles for selective oil absorption and oil/water separation

Three-dimensional superhydrophobic/superoleophilic materials (3D-HOMs) with remote controllability are highly desirable for water remediation. Herein, a new monolithic silica sponge decorated with hierarchical cobalt (Co) nanoparticles that fulfils almost all major requirements and applications for water remediation was fabricated by self-assembly electrospinning, controlled particle precipitation, and subsequent surface coating. Attributing to the continuous silica fibers and the hierarchical Co microstructures, the modified silica sponge (MSS) possesses excellent superhydrophobicity and oil selectivity, low bulk density (49 mg/cm3), high surface area (8.7 m2/g) and absorption capacity (45–91-fold weight gain), ultrahigh thermal resistance (tolerance to liquid nitrogen and combustion), flexibility, deformability, durability, and remote controllability through magnetic field manipulation. Moreover, simply compacting MSS can easily enhance its separation efficiency by bringing the interior structures to the contacting interfaces, which solves the performance deterioration issue over time for most 3D-HOMs. With all of these satisfactory properties, MSSs can be used as both durable magnetic superabsorbers and efficient oil/water separation filters with a long life span.

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.

Self-cleaning superhydrophobic epoxy coating based on fibrous silica-coated iron oxide magnetic nanoparticles

Inspired by the self-cleaning lotus leaf, a facile method of fabricating superhydrophobic silica coated magnetite nanoparticles using a cost-effective process is presented in this work. The structural characterizations and magnetic properties of the obtained core-shell magnetic nanoparticles were characterized by means of X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). TEM analysis revealed that the particles present flower‐like dendrimeric fibers morphology. The particles were uniformly dispersed on the surface of an epoxy resin coating with the purpose to increase the roughness and reduce the surface energy of the surface. The resulting superhydrophobic surface provides robust water-repellent surface under harsh conditions, thanks to its self-cleaning characteristic. The superhydrophobicity of this surface was confirmed based on the measurements of a water contact angle around 175°, which surpasses the theoretical limit of the superhydrophobicity. The simplicity and the cost-effectiveness of the process developed in this study appears to be a promising route for the preparation of other magnetic superhydrophobic organic-inorganic hybrid materials that would be beneficial in a wide variety of applications.

Transparent superhydrophobic surfaces using a spray coating process

One significant maintenance problem and cost associated with solar energy conversion systems is the soiling due to the accumulation of dust and other pollutants. In this work, we describe a scalable approach for applying antisoiling coatings based on superhydrophobic (SH) silica particles using a spray coating process. A large water contact angle (WCA) is one of the characteristics of excellent SH surfaces and because of the low surface energy and low adhesion forces the soiling rate is reduced. Our findings indicate that the WCA depends strongly on the ratio of the polymer binder and the nanoparticles. The nanoparticle surface coverage of the spray coated samples was substantially improved after rinsing with solvent. This process tended to remove large aggregates and excess polymer binder and further increased the WCA by allowing exposure of the functionalized nanoparticles. The durability of the SH coatings was enhanced when the substrate was pretreated with polymer binder and an optimal curing time between 30 and 60min. The abrasion tests of the SH coatings we report in this study showed that the WCA decreased from ~ 166° to ~ 157° after exposure to 2.6g of sand. Such coatings will help reduce costs of periodic cleaning of solar energy conversion systems (photovoltaic panels and concentrated solar mirrors).

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.

A Facile Cost-effective Method for Preparing Superhydrophobic Self-cleaning Silica Nanoparticles Coating on Al Substrate

Aluminum and its alloys have achieved extensive industrial application while contamination can cause serious problems to their aesthetic appearance and functionality. Superhydrophobic coating could be a potential solution to the problems. In this study, superhydrophobic coating on the Aluminum alloy surface was prepared via spraying hydrophobic silica nanoparticles suspension. The static water contact angle and sliding angle on the silica nanoparticle deposited aluminum alloy surface were 159±1° and 2°, respectively. In addition, the silica nanoparticle deposited aluminum alloy surface showed excellent self-cleaning property. This method may provide a facile and cost-effective route to form surperhydrophobic surfaces, which would be of technological significance for many practical applications.

A superhydrophobic silica aerogel with high surface area for needle trap microextraction of chlorobenzenes

The authors have synthesized a superhydrophobic silica aerogel by using a sol-gel technique. The material is shown to be an efficient sorbent for needle trap microextraction of chlorobenzenes. Hydrophobicity affects the performance of the sorbent as shown by altering the ratio between tetraethylorthosilicate (TEOS) and methyltrimethoxysilane when synthesizing the sorbent. The observed contact angle (which is >150°) underpins the superhydrophobic properties of the aerogel. The microstructure of the sorbent was investigated by BET adsorption, revealing a surface area above 1000 m2 g−1. The sorbent was applied to needle trap extraction of chlorobenzenes from aqueous samples, and their subsequent determination by GC/MS. The effects of extraction temperature and extraction time, ionic strength, desorption temperature and time were optimized. The method has a detection limit range of 0.4–1.1 ng mL−1, and quantification limits from 2.2 to 7.3 ng L−1. The relative standard deviations (at a level of 10 ngL−1) are between 4 and 8% (for n = 3). The calibration plots for chlorobenzenes are linear in the 2 to 100 ng L-1 concentration range. The method was successfully applied to the analysis of water samples, and relative recoveries were between 88 and 109%.

Fluorine free superhydrophobic surface textured silica particles and its dynamics–Transition from impalement to impingement

Abstract We report a facile method towards synthesis of fluorine free superhydrophobic mesoporous silica particles. Silica particles were prepared from rice husk (RH) as the silica source and CTAB as the structure directing agent. The as-prepared hydrophilic silica particles were converted to superhydrophobic structures by silane treatments. Silane treatment enhanced the wetting nature of the silica material from 60° to

Robust superhydrophobic candle soot and silica composite sponges for efficient oil/water separation in corrosive and hot water

The superhydrophobic sponges were fabricated through dip-coating candle soot (CS) and SiO2 nanoparticles on polyurethane (PU) sponges. The as-prepared sponges exhibited high absorption capacity for oils and organic solvents and the separation efficiencies of oil/water mixtures were all higher than 99.00%. In addition, the CS-SiO2-PU sponge with robust superhydrophobicity could selectively absorb oil from corrosive solutions, hot water (92 ± 2 °C), and ice/water mixtures at magnetic stirring. Furthermore, the as-prepared sponge connected with a vacuum system could remove oil from water continuously. Therefore, the CS-SiO2-PU sponge as a promising candidate can realize oil/water separation in harsh conditions. The CS-SiO2-PU sponges with robust superhydrophobicity toward harsh conditions could absorb oils from water quickly in a vacuum system.

Highly transparent fluorine-free superhydrophobic silica nanotube coatings

Transparent coatings with self-cleaning properties are required for protection of outdoor optical devices. Highly transparent, fluorine-free superhydrophobic coatings of silica nanotubes (SNT) on glass substrates are fabricated by using poly(dimethylsiloxane) (PDMS) as the silica source and multi-walled carbon nanotubes (MWCNTs) as the sacrificial template, following by hydrophobization through chemical vapor deposition (CVD) of cured PDMS. The influence of surface topography from SNT on the transparency and superhydrophobicity of the coatings is investigated. High transparency and excellent superhydrophobicity of the surface can be achieved by changing the concentration of PDMS (CPDMS) for SNT coatings as well as the amount of the cured PDMS (APDMS) for hydrophobization. The optimum coating has an average transmittance higher than 83% in the visible-light range (400–780nm), a water contact angle (CA) of 165° and a slide angle (SA) lower than 3°. When applied as protective cover, the glass substrate with superhydrophobic coating has little effect on the power generation efficiency of solar cells and has outstanding self-cleaning properties.

Polystyrene assisted superhydrophobic silica coatings with surface protection and self-cleaning approach

Abstract Both surface morphology and surface energy of solid surface conclude its wettability, either in Wenzel’s hydrophobic or Cassie–Baxter’s superhydrophobic wetting state. The superhydrophobic silica coatings were prepared by spin deposition technique from a mixture of hydrophobically modified silica particles and polystyrene. To enhance the adherency of the coating on the substrate and also to improve the durability of the coating, polymer is especially utilized in the coating solution. The durability of the superhydrophobic coating was confirmed by resistency towards water jet impact. The consequence of number of spin deposited layers on the wettability of the coatings was precisely studied. The static and dynamic water contact angle of 158° and 9° were achieved on the coating surface. Freely rolling spherical water drops on the non-wettable solid surface are favourable for the self-cleaning effect and so the prepared superhydrophobic coatings revealed superior self-cleaning performance. An anti-corrosion performance of the superhydrophobic coating was also confirmed using electrochemical corrosion experiments in 3.5% NaCl solution with long immersion time.

Superhydrophobic silica aerogels reinforced with polyacrylonitrile fibers for adsorbing oil from water and oil mixtures

Aerogels are modified by a simple method of hydrophobicity and mechanical properties simultaneously.

A silver nanoislands on silica spheres platform: enriching trace amounts of analytes for ultrasensitive and reproducible SERS detection.

The performance of surface-enhanced Raman scattering (SERS) for detecting trace amounts of analytes depends highly on the enrichment of the diluted analytes into a small region that can be detected. A super-hydrophobic delivery (SHD) process is an excellent process to enrich even femtomolar analytes for SERS detection. However, it is still challenging to easily fabricate a low detection limit, high sensitivity and reproducible SHD-SERS substrate. In this article, we present a cost-effective and fewer-step method to fabricate a SHD-SERS substrate, named the "silver nanoislands on silica spheres" (SNOSS) platform. It is easily prepared via the thermal evaporation of silver onto a layer of super-hydrophobic paint, which contains single-scale surface-fluorinated silica spheres. The SNOSS platform performs reproducible detection, which brings the relative standard deviation down to 8.85% and 5.63% for detecting 10-8 M R6G in one spot and spot-to-spot set-ups, respectively. The coefficient of determination (R2) is 0.9773 for R6G. The SNOSS platform can be applied to the quantitative detection of analytes whose concentrations range from sub-micromolar to femtomolar levels.