Facile fabrication of water repellent coatings from vinyl functionalized SiO2 spheres

Water repellent SiO₂ particulate coatings were prepared by a one-step introduction of vinyl groups on the coating surface. Rough surface structure and low surface energy could be directly obtained. Vinyl functionalized SiO₂ (vinyl-SiO₂) spheres with average diameter of 500 nm were first synthesized by a sol–gel method in aqueous solution using vinyltriethoxysilane as the precursor. The multilayer SiO₂ coating fabricated by dip-coating method was highly hydrophobic with a water contact angle of 145.7° ± 2.3°. The superhydrophobic SiO₂ coating with a water contact angle up to 158° ± 1.7° was prepared by spraying an alcohol mixture suspension of the vinyl-SiO₂ spheres on the glass substrate. In addition, the superhydrophobic SiO₂ coating demonstrated good stability under the acidic condition. However, it lost its hydrophobicity above 200°C because of the oxidation and degradation of vinyl groups.     

A simple method for the fabrication of silica-based superhydrophobic surfaces

The present article reports on a simple and convenient method for the fabrication of superhydrophobic surfaces based on silica particles by spraying the as-prepared silica suspension containing silica sol and silica microspheres on the substrate. The morphologies of the silica particulate coatings could be controlled by varying the silica microsphere concentration. The silica particulate coatings as prepared were exceptionally rough and superhydrophilic, with water contact angles less than 5°. The surface silanol groups of the hydrophilic coatings could be functionalized using 1H,1H,2H,2H-perfluorodecyltriethoxysilane to form hydrophobic groups. The resulting surface showed excellent superhydrophobic property with water contact angle up to 165.6 ± 0.9° and sliding angle of 3.5 ± 0.4°. In addition, the superhydrophobicity of the coating possessed a good stability after 3 months of exposure in air for a wide range of pH values.     

Superhydrophobic antireflective coating with high transmittance

The aim of this study is to fabricate a superhydrophobic antireflective (AR) coating that can be deposited on the covering of a solar cell system. First, AR coatings were synthesized on glass substrates with an average transmittance over 96% by layer-by-layer deposition of polyelectrolyte. Superhydrophobic sol gel was prepared by hydrolyzing tetraethoxysilane and then reacting it with hexamethyldisilazane. The sol gel, aged at 20°C for 96 h, was used to spin-coat a superhydrophobic film with a water contact angle of 163° and a transmittance of ~91%. The superhydrophobic sol gel was spin-coated on the top of an AR coating to form a superhydrophobic AR coating on a glass substrate. The average transmittance, advancing contact angle, and contact angle hysteresis of the superhydrophobic AR coating, which was spin-coated from sol gel aged for 96 h or 168 h, were 94.5 ± 0.7%, 154.0° ± 1.5°, and 15.4° ± 0.3° or 96.4 ± 0.2%, 158.4° ± 4.4°, and 1.8° ± 0.3°, respectively. Strategies for obtaining a superhydrophobic AR coating are discussed herein.     

Fabrication of mechanically robust superhydrophobic aluminum surface by acid etching and stearic acid modification

The aluminium surface with multi-scale structure has been fabricated via a facile and rapid solution-phase etching method by HCl/H₂O₂ etchants. After modification with stearic acid solution, the wettability of the etched aluminum surface turns into superhydrophobicity with an optimal water contact angle of 160° ± 2° and a sliding angle of 4° ± 1°. The processing conditions, such as the etching time, modifier types and the concentration of H₂O₂ are investigated to determine their effects on the surface morphology and wettability. As a result, the obtained sample shows excellent anti-adhesion property and bouncing phenomenon of water droplet. It can withstand mechanical abrasion for at least 100 cm under 12.3 kPa, or hydrostatic pressure under 24 ± 1 kPa without losing its superhydrophobicity, suggesting superior mechanical durability. Moreover, the surface also remains superhydrophobicity even after contacting corrosive liquids or long-term exposure in air over 100 days. Such a mechanically durable superhydrophobic aluminum surface can provide a promising practical application in various fields.     

Preparation of super‐hydrophobic film with fluorinated‐copolymer

Organic superhydrophobic films were prepared by utilizing TA‐N fluoroalkylate (TAN) and methyl methacrylate (MMA) copolymer as water‐repellent materials and inorganic silica powder as surface roughness material has been developed. Coating solutions prepared by adding silica powders into copolymer solution directly (one‐step method) and by adding silica powders into monomers and allowing them to react (two‐step method). The results showed that contact angles of the films prepared by one‐step method (37.6 wt % of silica powders in the coating solution) were greater than 150°, but the transmittance of the film at visible light was only 30%. On the other hand, the contact angle of films prepared by two‐step method (20 wt % of silica powders in the coating solution) was greater than 160° and the transmittance of the film was greater than 90%. The contact angle of the film prepared by poly(octyl acrylate), POA, was 32.1°, but while introducing silica powder into the system, the contact angle of the film was reduced to be smaller than 5°. Thus, superhydrophobic and superhydrophilic films can be obtained by introducing a roughening material on the hydrophobic surface and the hydrophilic surface, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1646–1653, 2007     

SYNTHESIS OF ACTIVATED CARBON FROM JATROPHA SEED COAT AND APPLICATION TO ADSORPTION OF IODINE AND METHYLENE BLUE

This article provides evidence that jatropha seed coat residues can be used as a carbon source for preparing activated carbons that have good adsorption properties for iodine and methylene blue. Activated carbons were prepared using three different methods of activation, physical, chemical, and physico-chemical, for a range of activation temperatures (600°, 700°, 800°, and 900°C) and activation hold times (1, 2, and 3 h). The highest BET surface area (1479 m² g^?1) and the highest iodine adsorption (1511 mg g^?1) were obtained with physico-chemical activation at a temperature of 900°C and a hold time of 2 h. This activated carbon gave higher BET surface area and iodine adsorption than commercial activated carbon (1169.1 m² g^?1 and 1076 mg g^?1). The activated carbons prepared by physico-chemical activation at 900°C and 2 h were then tested for adsorption of methylene blue at a range of concentrations of methylene blue (100, 200, 300, 400, and 500 mg L^?1). It was found that a Langmuir isotherm gave a better fit (R ² = 0.999) to the observed adsorptions than a Freundlich isotherm (R ² = 0.884). For the adsorption kinetics, a pseudo-second-order model gave a better fit (R ² > 0.998, Δq _e  = 3.7%) than a pseudo-first-order model (R ² ≈ 0.95, Δq _e  = 85.6%). These results suggest that chemisorption is the rate-controlling step for the adsorption of methylene blue. The experimental results show that jatropha seed coat is a lignocellulosic waste precursor for preparation of activated carbon that is an alternative source for preparation of commercial-grade activated carbons.     

Treatment of ramie fiber with different techniques: the influence of diammonium phosphate on interfacial adhesion properties of ramie fiber-reinforced polylactic acid composite

Ramie fiber-reinforced polylactic acid (PLA) composites were successfully prepared by hot compression molding. Different treatment techniques were used to modify the surface of ramie fiber. The influence of diammonium phosphate (DAP) on the interfacial adhesion between ramie fiber and PLA composites was investigated by the contact angle measurements, FTIR and SEM analyses. The contact angle measurement results showed that alkali treatment combined with DAP was very efficient in decreasing the hydrophilicity of fibers. After treatment, the hydrophilicity of untreated ramie fiber from 5.9 ± 1.3 decreased to 2.0 ± 0.8 mJ/m². The wettability of alkali/silane/DAP-treated ramie fiber/PLA composite was higher (95.4° ± 1.3°) than that of pure ramie fiber/PLA composite (87.3° ± 1.9°). The FTIR results were consistent with the wetting measurements as the increment of hydrophilicity. Thermal analysis indicated that DAP-modified ramie fiber/PLA composites exhibited a lower thermal decomposition temperature, unique decomposition behavior and more residual char formation at decomposition temperature. The tensile, flexural and impact properties of DAP-modified ramie fiber composites were comparable to those of untreated ramie fiber composite. Moreover, proper alignment and uniform distribution of ramie fibers within the PLA matrix were found to be excellent. The morphological structures observed by SEM showed that well-modified ramie fibers enhanced the failure of the PLA composites in tensile, flexural and impact tests.     

Enhancement of adhesion,mechanical strength and anti-corrosion by multilayer superhydrophobic coating embedded electroactive PANI/CNF nanocomposite

Traditional insulative coatings usually suffer from pitting corrosion in harsh corrosive environment. Herein, in this work, electroactive polyaniline/carboxylated carbon nanofiber (PANI/CNF) nanocomposite was prepared via in situ chemical polymerization and first incorporated into superhydrophobic coating with better barrier effect. Multilayer coatings were constructed by facial spraying using polyphenylene sulfide (PPS) and ethylene tetrafluoroethylene (ETFE) with gradient weight ratios as film-forming materials. The composite coating with 40 wt% ETFE in top layer (denoted as ETFE-40) possesses best superhydrophobicity and highest oleophobicity with water contact angle (CA) and glycerol CA of 160° and 155° as well as low water sliding angle (SA) and glycerol SA of 2.2° and 8.8°, respectively. The lotus-like nano/micro structures, low surface energy material ETFE and modification of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) should contribute to the superior liquid repellency. Especially, robust mechanical strength and durable anti-wettability are obtained with high WCA of 151° and glycerol CA of 147° after 8000 cycles abrasion. The composite coating also exhibits strong adhesion and superior self-cleaning. The enhanced electrochemical corrosion resistance of the coating in 3.5 wt% NaCl solution can be attributed to the outstanding barrier function of superhydrophobic surface and the passivation effect of electroactive PANI/CNF. This novel and effective coating system would definitely benefit the development of robust protective coating and promise wider engineering application.     

Superhydrophobic surfaces: a review on fundamentals,applications, and challenges

Superhydrophobicity is the tendency of a surface to repel water drops. A surface is qualified as a superhydrophobic surface only if the surface possesses a high apparent contact angle (>150°), low contact angle hysteresis (<10°), low sliding angle (<5°) and high stability of Cassie model state. Efforts have been made to mimic the superhydrophobicity found in nature (for example, lotus leaf), so that artificial superhydrophobic surfaces could be prepared for a variety of applications. Due to their versatile use in many applications, such as water-resistant surfaces, antifogging surfaces, anti-icing surfaces, anticorrosion surfaces etc., many methods have been developed to fabricate them. In this article, the fundamental principles of superhydrophobicity, some of the recent works in the preparation of superhydrophobic surfaces, their potential applications, and the challenges confronted in their new applications are reviewed and discussed.     

Facile preparation of robust superhydrophobic surface based on multi-scales nanoparticle

A new superhydrophobic surface based on multi-scales nanoparticle was designed and prepared to enhance the robustness and reproducibility. The influence of multi-scale nanoparticles on the structure and property of the superhydrophobic surface was further investigated. The superhydrophobic surface with optimized composition did not only show high contact angle of 160°-166.3° but also exhibited good durability to the mechanical, chemical, and thermal environments. Furthermore, the superhydrophobic surface was evaluated for application in anticorrosion, anti-icing, and self-cleaning. This study provides a new method to prepare robust superhydrophobic surface based on polymer nanocomposite coating for various potential applications.     

A comparative structure–property study of polyphosphazene micro-nano spheres

Novel fluorinated cross-linked polyphosphazene micro-nano spheres have been prepared by precipitation polymerization of hexachlorocyclotriphosphazene (HCCP) monomer. The influence of molecular structure on the morphology of polyphosphazene micro-nano spheres was investigated by SEM and TEM. The micro-nano spheres were also characterized by Fourier transforms infrared, X-ray photoelectron spectroscopy and thermo gravimetric analysis. The results indicate that the 5 % thermal degradation temperature is 366 °C. It was found that a silicon wafer dip-coated with thus prepared micro-nano spheres has a water contact angle as high as 137° ± 1.5°. Furthermore, the effects of the concentration of HCCP and ultrasonic power on the morphology were also discussed.     

Fabricating translucent polydimethylsiloxane (PDMS) super-hydrophobic surface greenly by facile water-dissolved fillers

In this study, a polydimethylsiloxane (PDMS) colloid was cast onto a template made of recycled polypropylene for structural duplication to fabricate translucent super-hydrophobic surfaces greenly without the use of any complicated method. The surface structure of the template was formed by hot embossing using salt grain fillers dissolved in water. The resulting contact angle (CA) values of fabricated PDMS surfaces were 153.4 ± 0.6°, 152.3 ± 1.8°, 152.2 ± 0.8°, and 152.0 ± 1.6° and the associated slide angle (SA) values were 5.8 ± 0.6°, 8.7 ± 1.5°, 8.6 ± 1.1°, and 16.3 ± 1.9° for filler grain size categories A, B, C, and D, respectively. The surfaces with grain sizes A, B, and C exhibited super-hydrophobic conditions, where CA > 150° and SA < 10°; on the other hand, the surface with grain size D exhibited an SA value greater than 10°. The measured percentages of light transmittance in the visible wavelength range of 400–800 nm were 75–80% for grain sizes B, C, and D and 85–90% for grain size A. Furthermore, a green laser light was diffused from a spot of 0.5–7.7 cm in diameter; related glare was also eliminated.     

Injection-molded plastic plate with hydrophobic surface by nanoperiodic structure applied in uniaxial direction

The purpose of this research is to establish a processing method for a wide-area nanometer scale periodic structure on the surface of a plastic plate in order to improve its hydrophobicity. We also evaluated the effect of a nanoperiodic structure applied in the uniaxial direction. Plastic plates of acrylonitrile–ethylene–styrene with dimensions of 100 × 100 mm² with a nanoperiodic structure on their surfaces were fabricated using a femtosecond laser and an injection molding technique. In the injection molding, the maximum transfer ratio for the depth reached as high as 0.79. When the nanoperiodic structure was applied in the uniaxial direction, the apparent contact angles did not decrease with respect to the direction of the ridges. As a result, the apparent contact angle increased by 20.4°, from 77.2° to 97.6° which is equivalent to 26%. In the six-month duration test, the sliding angle was initially decreased by applying the nanoperiodic structure. Additionally, the sliding angle was maintained between 20° and 38.3° during the duration test, which was lower than the angle for the flat plate at 42.7°. It can be considered that the depth was sufficient to maintain the sliding angle. In this condition, the contact angle hysteresis did not differ with or without the nanoperiodic structure on the surfaces, an effect that could be caused by surface dirt. In summary, the plastic plate was well drained and the characteristics were maintained for several months by forming the nanoperiodic structure on the surface.     

Coconut kernel-derived activated carbon as electrode material for electrical double-layer capacitors

Carbonization of milk-free coconut kernel pulp is carried out at low temperatures. The carbon samples are activated using KOH, and electrical double-layer capacitor (EDLC) properties are studied. Among the several samples prepared, activated carbon prepared at 600 °C has a large surface area (1,200 m² g^?1). There is a decrease in surface area with increasing temperature of preparation. Cyclic voltammetry and galvanostatic charge–discharge studies suggest that activated carbons derived from coconut kernel pulp are appropriate materials for EDLC studies in acidic, alkaline, and non-aqueous electrolytes. Specific capacitance of 173 F g^?1 is obtained in 1 M H₂SO₄ electrolyte for the activated carbon prepared at 600 °C. The supercapacitor properties of activated carbon sample prepared at 600 °C are superior to the samples prepared at higher temperatures.     

Axial wall height effect on failure of adhesively luted computer assisted design/computer assisted manufactured ceramic crowns on preparations containing advanced total occlusal convergence

Computerized dentistry advocates promote that CAD/CAM adhesive technology compensates for traditional crown preparation recommendations. This study was to investigate the effect of preparation axial wall height on retention of adhesively-luted, all ceramic crowns manufactured by computerized methods. Maxillary molars were prepared with a 20 ° total occlusal convergence with preparation axial wall heights of 4, 3, 2, and 1 mm as well as an additional group containing a flat surface. The preparations were scanned with a computer acquisition device with crowns milled and prepared from a lithium disilicate ceramic material. The crowns were adhesively luted to the prepared tooth surfaces and then tested under static loading at a 45 ° angle to the tooth long axis on a universal testing machine until failure. Analysis with Kruskal-Wallis/Dunn’s found that crowns with 2, 3, and 4 mm preparation axial wall height had similar failure loads and demonstrated significantly greater failure load resistance than the zero and 1 mm axial wall height groups. However, failure mode analysis revealed that the 2 mm axial wall height group demonstrated universal adhesive failures as the zero and 1 mm axial wall height groups. Under the conditions of this study, some evidence is provided that adhesive technology may provided some compensation for less than optimal preparation features as the 3 mm axial wall height preparations demonstrated equivalent failure mode as the recommended 4 mm axial wall height preparations. However, further fatigue studies are warranted.     

Comparison of methanol/hydrochloric,ferric chloride acid versus tribochemical silica coating for adhesion of resin cement to zirconium dioxide

This study compared air-abrasion and etching regimens on adhesion of resin luting agent to zirconium dioxide. Ceramic specimens (LAVA, 3 M ESPE) (N = 16) were embedded in acrylic resin and exposed surfaces were polished. The specimens were randomly assigned into four groups (n = 12, 3 specimens for each disc): SC: Air-borne particle abrasion (30 μm aluminum oxide particles coated with silica, CoJet, 3 M ESPE); MH: Heated chemical solution (Methanol-800 mL; 37% Hydrochloric Acid-200 mL; Ferric Chloride-2 g) at 100 °C for 30 min, MHP: Primer (Metal/Zirconia Primer, Ivoclar Vivadent) + MH, P: Primer only (Metal/Zirconia Primer). Cylindrical molds (internal diameter: 0.7 mm; height: 1.5 mm) were placed on each conditioned specimen, filled with resin cement (Multilink Automix) and photo-polymerized for 60 s. After 24 h, the molds were removed and the specimens were stored in distilled water at 37 °C for six months). Microshear test was performed in a Universal Testing Machine (1 mm/min). Failures types were classified as adhesive, mixed, or cohesive. In another set of specimens (n = 2 per group) contact angle measurements were recorded. Data were analyzed statistically using Kruskal–Wallis and Dunn’s tests (α = 0.05). The surface conditioning method significantly affected the mean bond strength (MPa) (p < 0.0001): SC(18.3 ± 0.3)^a < P(5.00 ± 0.07)^b < MHP(4.7 ± 0.08)^c < MH(0.84 ± 0.01)^c. While Group SC showed mainly adhesive (58%) and mixed (41.7%) failure types, groups MH, MHP, and P presented exclusively adhesive failures. SC, MHP, and P (29–32°) showed lower contact angle than MH (78.9°). Volume loss was the highest with MHP (9.92 μl) followed by SC (9.67 μl).     

Effect of femtosecond laser beam angle and formed shape on surface roughness and shear bond strength between zirconia and resin cement

Achieving adhesion between resin cement and zirconia requires pretreatment of the surface. This in vitro study aimed to evaluate the effect of femtosecond laser beam angle and the shape of the formed surfaces, on the roughness and shear bond strength (SBS) of resin cement to zirconia ceramic. Seventy Y-TZP ceramic specimens were divided into seven groups (n = 10). A femtosecond laser irradiation was performed on the ceramic surface of three shapes (spiral (SP), square (SQ) and circular (CI) and at two angles (30 and 90°) to give SP-30, SQ-30 and CI-30 and SP-90, SQ-90 and CI-90, respectively. After treatment, the surface roughness of all specimens was evaluated using a profilometer. One specimen from each group was analysed using a scanning electron microscope. The bonded specimens were thermocycled 5000 times and then an SBS test was performed. Kruskal-Wallis and Mann-Whitney U tests were used to analyse surface roughness and SBS values. The control group had statistically lower surface roughness (R_a) values than the treated groups (p < 0.05). SP-30 and SQ-30 laser treated specimens showed higher R_a values than the other specimens. Statistically significant SBS values (p = 0.000) were observed between the groups. All laser treated samples showed greater SBS compared to the control group. SP-30, SQ-30 and SQ-90 groups showed the highest SBS values. Within the limitations of this experimental study, the highest mean values for R_a and SBS were achieved with SP and SQ surfaces using a 30° angle laser beam.     

Synthesis and characterization of poly(methyl methacrylate)/polysiloxane composites and their coating properties

A series of poly(methyl methacrylate) (PMMA)/polysiloxane composites and their coatings were prepared as designed. A copolymer (PMMAVTEOS) containing methyl methacrylate (MMA) and vinyltriethoxysilane (VTEOS) was prepared by free radical polymerization and then condensed with methyl triethoxysilane (MTES) to fabricate PMMA/polysiloxane composites; their corresponding coatings were obtained via a curing process in an oven (at 75 °C). The polymers were characterized by gel permeation chromatography and Fourier transform infrared spectroscopy. The surface property, hardness, water contact angle, thermal stability, and optical property of the coatings were investigated by scanning electron microscopy, pencil hardness testing, water contact angle testing, thermogravimetric analysis, and ultraviolet–visible spectroscopy, respectively. The results showed that, after addition of MMA, the pencil hardness of the coatings was reduced from 6H to 2H and the thermal stability decreased from 365 to 314 °C. However, it increased the flexibility and adhesion properties (the water contact angle increased from 94.7° to 102.1°). The transparent PMMA/polysiloxane coatings showed excellent scratch resistance, a smooth surface, high thermal stability, and a strong adhesion property. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46358.     

Ultrahydrophobic silica films by sol–gel process

Wettability of solid surfaces is a crucial concern in our daily life as well as in engineering and science. The present research work describes the room temperature (27 °C) synthesis of adherent and water repellent silica films on glass substrates using vinyltrimethoxysilane (VTMS) as a hydrophobic reagent by a single step sol–gel process. The silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), water (H₂O) constant at 1:14.69:5, respectively, with 0.01 M NH₄F throughout the experiments and the VTMS/TEOS molar ratio (M) was varied from 0 to 0.97. The effects of M on the surface structure and hydrophobicity have been researched. The static water contact angle as high as 144° and water sliding angle as low as 14° was obtained for silica film prepared from M = 0.97. The hydrophobic silica films retained their hydrophobicity up to a temperature of 255 °C and above this temperature the films became superhydrophilic. The prepared silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity test and static and dynamic water contact angle measurements.     

Could readily silanized silica particles substitute silica coating and silanization in conditioning zirconium dioxide for resin adhesion?

This study investigated the effect of particle types with different morphology and surface properties on the wettability and adhesion of resin cement to zirconia. Zirconia specimens (5 × 5 × 1 mm³) were wet polished. Specimens were randomly assigned to one of the following protocols (N = 36, n = 9 per group): Group CON: Control, no surface conditioning; Group AL: Chairside air-abrasion with aluminium trioxide (50 μm Al₂O₃) + silane; Group SIL: Chairside air-abrasion with alumina particles coated with silica (SIL) (30 μm SiO2, SilJet) + air-drying + silane; Group 4: Chairside air-abrasion with readily silanized silica particles (SILP) (30 μm SiO_2, SilJet Plus). Adhesive resin was applied and resin cement (Variolink II, Ivoclar) was bonded using polyethylene moulds and photo-polymerized and aged (thermocycling, 6.000 cycles, 5–55 °C). Shear bond test was performed using Universal Testing Machine (1 mm/min). Pretest failures were considered 0 MPa. Contact angle measurements were performed (n = 2/group, sessile drop with water). Data (MPa) were analyzed (ANOVA, Tukey’s (α = 0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m) and shape (0), values were calculated. Contact angle measurements were in descending order as follows: SIL (74°)^c < CON (60°)^c < AL (51°)^b < SILP (40°)^a. Bond strength (MPa) with SIL (17.2 ± 4)^a and SILP (17.3 ± 1.9)^a demonstrated no significant difference (p > 0.05), being higher than AL (8.4 ± 1.5)^b and CON (0)^c (p < 0.05). Failure types were exclusively adhesive in all groups. Weibull distribution presented the highest shape (0) for SILP (10.8). SILP presented better wettability than AL. SILP provided similar bond strength to SIL. Readily silanized silica particles may substitute for conventional silica coating and silanization.