Papers by Keyword: Superhydrophobicity

Abstract: Black limestones were used as structural and ornamental stones in the facades of the four madrasas at Sultan Hasan mosque. Regrettably, the studied black limestone blocks have significantly suffered from deterioration mechanisms, causing severe damage forms such as discolouration, salt crystallization, cracking, fissuring, flaking, granular disintegration, and microbial growth. Examination and analysis of the studied black limestone were performed using polarizing light microscope, scanning electron microscope equipped with EDS, X-ray diffraction, and fungal investigation. The current research mainly presents an experimental study to evaluate the efficiency of nanocomposites prepared from SRC-220 (fluorinated polyurethane) and TiO₂ NPs in the treatment of the studied black limestone. The prepared TiO₂ nanocomposites were used for the treatment of experimental black limestone samples. The effect of TiO₂ nanoparticle concentration on the properties of the fabricated nanocomposites was comparatively tested. Experimental study was implemented using transmission electron microscope, scanning electron microscope, atomic force microscope, static water contact angle, colourimetric investigation, abrasion resistance, self-cleaning activity, and fungistatic efficiency. The results proved that the addition of TiO₂ nanoparticles into SRC-220 pure polymer produced multifunctional nanocomposites characterized by high transparency, good consolidation effect, superhydrophobicity, self-cleaning, and antifugal efficiency. Moreover, it was demonstrated that the concentration of TiO₂ nanoparticles significantly affects the obtained properties of the prepared nanocomposites.

Abstract: The thermal stability of the superhydrophobic properties of coatings obtained on a magnesium alloy by plasma electrolytic oxidation (PEO) followed by treatment with fluoropolymer was studied. It was established that formed surface layers have contact angle (CA) equal to 171° and contact angle hysteresis equal to 6° at 25 °C, which allows to characterize them as superhydrophobic. After 5 cycles of cooling-heating of composite layers, CA was 135°, indicating the durability of coatings. Additionally, obtained polymer-containing layers demonstrated low wettability at 0 °C (CA was 105°).

Abstract: The paper presents results of the composite polymer-containing layers formation by plasma electrolytic oxidation (PEO) with subsequent application of the superdispersed polytetrafluoroethylene (SPTFE) aqueous suspension. The corrosion properties and adhesion of coatings have been investigated using potentiodynamic polarization and scratch tests. Incorporation of SPTFE decreased the corrosion current density for composite layers by more than 3 orders of magnitude in comparison with the base PEO-coating and increased the coatings adhesion by 30 %.

Abstract: The paper presents the results of a study of the protective properties of composite coatings obtained on AMg3 aluminum alloy by plasma electrolytic oxidation (PEO) and subsequent modification of formed oxide layer with superdispersed polytetrafluoroethylene (SPTFE) from a suspension based on isopropyl alcohol. The incorporation of fluoropolymer decreased the porosity of base PEO-coating more than one order of magnitude. Formed composite layers increased wearproof of the samples by more than two orders of magnitude in comparison with PEO-coating. Additionally, polymer-containing coatings has higher adhesion compared to substrate. Formed composite layers possess superhydrophobic properties: contact angle attains 155°.

Abstract: Oil-water separation has become the prime concern for fossil fuel exploration industries. In the present study, superhydrophobic coating on filter paper was prepared to repellent water while allowing oil to flow freely from its porous structures. Coating was generated by solution-casting technique on cellulosic filter paper using silica nanoparticles (SiO₂) along with silane coupler hexadecyltrimethoxysilane (HDTMS). The contact angle was measured, and it has shown 175.1° ± 1.5°, and the tilting angle is 1.5° ± 0.2°. The surface topography of coated and treated samples was also examined. Furthermore, thermal stability of fabricated filter papers was evaluated by annealing at a different range of temperatures (20 °C-220 °C). The pH resistance of the coatings were inspected by immersing the specimens in acidic and alkali solutions (pH 2-13). The mechanical durability was examined by tape-peeling and abrasion tests. Moreover, these samples have shown waterjet impact resistance. Filtration study was performed on coated filter papers using various oil-water mixtures of kerosene-water and petroleum ether-water and results have shown the separation efficiency of 99% and 98.5%, respectively. Thus these filter papers can have potential practical and industrial applications.

Abstract: Nature-inspired superhydrophobic surfaces have received immense industrial and academic interest due to their non-wettability and self-cleaning properties. To fabricate superhydrophobic silicone rubber surfaces, a simple, environmentally friendly atmospheric-pressure plasma treatment was applied. The effect of diverse plasma processing parameters on the final wettability behavior of the substrates, including plasma power, plasma frequency, number of passes, plasma jet speed, plasma cycle time and distance between the nuzzle outlet and substrate, were analyzed by means of design of experiments (DoE). Surface chemical characterization illustrated the influence of plasma treatment on the chemical composition of the produced silicone rubber. Furthermore, the presence of microstructures as well as the chemical composition of the surface was confirmed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analysis.

Abstract: A facile method is introduced for production of micro-nanostructured silicone rubber surfaces by means of direct replication using a compression molding system. The fabricated samples possessing surface roughness display water contact angle of more than 160o and contact angle hysteresis (CAH) and sliding angle of less than 5o. Such low surface wettability of silicone specimens verifies the induced superhydrophobic property. Chemically etched aluminum surfaces could work excellently as templates whose patterns were replicated on the rubber surfaces successfully. Various etching conditions were examined. Surface characterization techniques revealed the presence of micro-nanostructures on the produced silicone surfaces.

Abstract: Industrial application of superhydrophobic surfaces is limited by the unsatisfactory mechanical properties of the material. Combining chemical etching and anodization terraced features containing aluminium oxide on different aluminium alloy surfaces were produced. After modified by fatty acid, the surfaces were superhydrophobic and they showed self-cleaning effect. The highest contact angle was obtained after forming hierarchical structures with a solution free of fluorine compounds; therefore, the process is considered eco-friendly. The alumina formed in the coating process promotes an improved corrosion resistance. The present study has three main objectives: to identify the molecules responsible for superhydrophobicity, the mechanism by which superhydrophobicity is produced, and consequently the influence of variables such as anodization time on the proposed processing method. We use time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) techniques to identify each compound involved in the final surface, by paying close attention to the analysis of the mechanism by which the chemical reaction proceeds. The morphology of the superhydrophobic surfaces was further observed by scanning electron microscope (SEM) and atomic force microscopy and was used to elucidate the effect of the anodization time in the properties of the superhydrophobic material.

Abstract: Accurate characterization of the underwater stability of superhydrophobic surfaces is crucial for the design of durable anti-fouling materials and advanced microfluidic concepts. Although superhydrophobic breakdown is a major issue that hampers full exploitation of superhydrophobic functional materials, suitable characterization methods are lacking and relatively little is known about the wetting dynamics. In this work we explore a novel method based on attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) for large-area in-situ analysis of wetting states and wetting transitions on nanostructured surfaces. Spontaneous wetting is induced on superhydrophobic silicon nanopillars through in-situ modulation of the liquid composition and surface tension. The high surface sensitivity of ATR-FTIR enables quantitative evaluation of the instantaneous liquid composition and wetted area. Critical transition criteria for superhydrophobic breakdown are assessed using both ATR-FTIR and goniometric measurements. Significant deviations from classical wetting models are revealed, emphasizing the need for more accurate transition criteria and careful experimental validation. Breakdown kinetics near the critical transition are found to be significantly slowed down on nanostructured surfaces, which underlines the necessity for accurate characterization of wetting dynamics at the nanoscale. The proposed ATR-FTIR method can be promising for dynamic studies of wetting transitions on more advanced surfaces, as hierarchical structures or oleophobic designs.

Abstract: A latex cup is used to collect latex from a rubber tree which is an economic plant in Thailand. The fresh latex or crude rubber consists of organic compound and water which can wet and adhere to surface of the collecting cup. In this research, surface of the latex cup was treated with polymethylhydrogen siloxane-functionalized silica compound to improve hydrophobicity so that it could repel the dirt and latex, resulting in an anti-adhesion between the latex and the cup. Surface of the latex cup was etched with 10 % v/v hydrofluoric acid for 30 min before application of the siloxane coating which was performed by immersion in the solution, painting and spraying, respectively. The result revealed that the immersion method exhibited optimum property justified by high value of water contact angle, low surface free energy, surface roughness and the field test. At the optimum polymethylhydrogen siloxane : fumed silica ratio of 3 : 1 wt%, the treated sample had water contact angle of 139.24 ± 0.78 degrees and possessed surface energy of 1.07 mJ/m². The field test conducted in the rubber field in Trang province revealed good durability of the coating. The water contact angles were 132.15 ± 2.05 and 129.20 ± 2.34 degrees after 2 weeks and 1 month, respectively, of the field service.