Properties Of Superhydrophobic Surfaces Research Articles

Superhydrophobic surfaces based on self-organized TiO2-nanotubes

Abstract In this study, the interaction between a self-organized TiO 2 -nanotube layer formed by an anodizing procedure and a post-treatment with different water repellent coatings is investigated. Therefore, a conceptional model of these interactions is experimentally explored. Ti6Al4V samples are anodized using a fluoride-containing electrolyte. Using an anodizing voltage of 30 V, a homogeneous layer of TiO 2 -nanotubes with a pore diameter of 68.1 ± 3.8 nm and oxide layer thickness of 589.2 ± 23.7 nm could be generated on the surface. The anodization increases the surface area in comparison to the original state. To achieve water repellent surface properties the TiO 2 -nanotubes are functionalized by a selection of coating systems. Two different coating systems (coating 1: fluoroalkylsilane based; coating 2: perfluoropolyether based) are investigated within this study. By means of physical and chemical analyses both morphology and composition of the TiO 2 -nanotube surface are characterized. The scanning electron microscope (SEM) analyses illustrate that the tube morphology is not covered by the different coating systems. The chemical composition of the two different coatings is investigated by X-ray photoelectron spectroscopy (XPS). The results indicate that only the boundaries of the TiO 2 -nanotubes are covered by the coatings. However, the XPS results reveal that the different coatings do not fully infiltrate the tubular structures. Only the first nanometers (15–20 nm) are covered. To characterize and evaluate the superhydrophobic properties of the modified surfaces, the dynamic contact angles are measured. Each individual coating system shows a contact angle in excess of 150°. Surfaces that are simply degreased in an alkaline solution, without post-treatment with a water repellent coating show a contact angle of 21.9 ± 5.4°. Hence, it becomes evident that only the combination of a surface nanostructuring and a water repellent coating leads to superhydrophobic surface properties.

Superhydrophobic surface properties with various nanofibrous structures by electrodeposition of PEDOT polymers with short fluorinated chains and rigid spacers

In the aim to produce superhydrophobic surface properties, the nanofibers are excellent candidates due to the possible control in the water adhesion by the nanofiber characteristics, for example. Here, we report the growth of nanofibers with various assemblies directly on surfaces by electropolymerization. For this purpose, an original 3,4-ethylenediothiophene monomer was synthesized. The monomer contains a short fluorinated chain (C4F9) in order to preserve the nanofiber morphology and a highly rigid methoxybenzothioate spacer for the reduction of the mobility. In this work, we show that various nanofibrous structures and superhydrophobic properties can be obtained by modifying the electrolyte while the surface roughness can also be controlled by the number of deposition scans. The nanofibrous polymers could be used to control the attachment and growth of cells or bacteria.

Surfactant-Free and Controlled Synthesis of Hexagonal CeVO4 Nanoplates: Photocatalytic Activity and Superhydrophobic Property.

Nanomaterials with both superhydrophobic surface properties as well as photocatalytic activities could have important industrial applications. Herein, we synthesized CeVO4 nanocrystals with hexagonal nanoplate structures from the reaction of decavanadate (K6V10O28⋅9 H2O) and CeCl3⋅H2O precursors via a hydrothermal method. This synthetic route has four advantages: 1) the reaction condition is relatively mild, 2) it doesn′t need surfactants or templates, 3) it requires no expensive equipment, and 4) products are of higher purity. During synthesis, solution pH, and reaction temperature were found to play important roles in determining the growth process and final morphologies of the CeVO4 products. These products were characterized spectrophotometrically and via scanning and transmission electron microscopy. Furthermore, the wettability of the as-synthesized film CeVO4 nanoplates was studied by measuring water contact angle (CA). The largest CA measured was at 169.5 ° for a glass substrate treated with 0.06 g mL−1 CeVO4 followed by 2 % 1 H, 1 H, 2 H, 2 H-perfluorodecyltriethoxysilane. Finally, the CeVO4 nanoplates exhibited excellent photocatalytic activity in degradation of rhodamine B (RhB) under UV irradiation and was stable even after repeated cycles of use.

Fabrication and anti-icing property of coral-like superhydrophobic aluminum surface

Aluminum is one of the most widely used metals in transmission lines. Accumulation of ice on aluminum may cause serious consequences such as tower collapse and power failure. Here we develop a method to fabricate a coral-like superhydrophobic surface to improve its anti-icing performance via chemical etching and hot-water treatment. The as-prepared surface exhibited superhydrophobicity with a contact angle (CA) of 164.8±1.1° and the sliding angle smaller than 1°. The static and dynamic anti-icing behaviors of the superhydrophobic surface in different conditions were systematically investigated using a self-made device and artificial climate laboratory. Results show that the coral-like superhydrophobic structure displayed excellent anti-icing property. The water droplet remained unfrozen on the as-prepared surface at −6°C for over 110min. 71% of the surface was free of ice when exposed in “glaze ice” for 30min. This investigation proposed a new way to design an anti-icing surface which may have potential future applications in transmission lines against ice accumulation.

Influence of different chemical modifications on the icephobic properties of superhydrophobic surfaces in a condensate environment

The icephobic properties (both in ice-adhesion reduction and water rebound) of different superhydrophobic surfaces varied wildly at sub-zero condensate environment.

초소수성 표면특성을 갖는 폴리프로필렌 박막형성

The effects of process parameters for the formation of polypropylene film such as the polypropylene concentration in the solution, drying temperature for coating film, and variation of nano-silica content on the surface structure and property of polypropylene film have been studied. A super-hydrophobic polypropylene film with a maximum contact angle of 154° was obtained at the condition of a polypropylene concentration of 30 mg/mL, a drying temperature of 30 ℃, a drying pressure of 93 mtorr for 90 min. The increase of a drying temperature reduced the contact angle by enhancing the surface smoothness of the film. The increase of nano-silica content in the composite film composed of polypropylene and silica changed the surface shape from microporous to microglobular, which led to increasing the contact angle and showed the super-hydrophobic surface property.

Combining hierarchical surface roughness with fluorinated surface chemistry to preserve superhydrophobicity after organic contamination

Surfaces exhibiting superhydrophobicity are attracting commercial and academic attention because of their potential applications in, for example, self-cleaning utensils, microfluidic systems, and microelectronic devices. In this study, we prepared a fluorinated superhydrophobic surface displaying nanoscale roughness, a superhydrophobic surface possessing a micro- and nanoscale binary structure, and a fluorinated superhydrophobic surface possessing such a binary structure. We investigated the effects of the (i) hierarchy of the surface topography and (ii) the surface chemical composition of the superhydrophobic carbon nanotube/polybenzoxazine coatings on their ability to retain superhydrophobicity upon contamination with particles and organic matter, an important characteristic for maintaining non-wetting properties under outdoor conditions. We have found that the topographical microstructure and the surface chemical composition are both important factors for preservation of the non-wetting properties of such superhydrophobic surfaces upon contamination with organic matter.

Low temperature self-cleaning properties of superhydrophobic surfaces

Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of −10°C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of −12°C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.

Superhydrophobic mesoporous silica nanospheres achieved via a high level of organo-functionalization.

We report an efficient method for the synthesis of organo-functionalized mesoporous silica nanospheres (MSNs) with high-level organo-functionalization using TEOS and chlorosilanes as precursors. The phenyl-functionalized MSNs with superhydrophobic surface properties could efficiently adsorb organic pollutants from water.

Interfacial Effects of Superhydrophobic Plant Surfaces: A Review

Nature is a huge gallery of art involving nearly perfect structures and properties over the millions of years of development. Many plants and animals show water-repellent properties with fine micro-structures, such as lotus leaf, water skipper and wings of butterfly. Inspired by these special surfaces, the artificial superhydrophobic surfaces have attracted wide attention in both basic research and industrial applications. The wetting properties of superhydrophobic surfaces in nature are affected by the chemical compositions and the surface topographies. So it is possible to realize the biomimetic superhydrophobic surfaces by tuning their surface roughness and surface free energy correspondingly. This review briefly introduces the physical-chemical basis of superhydrophobic plant surfaces in nature to explain how the superhydrophobicity of plant surfaces can be applied to different biomimetic functional materials with relevance to technological applications. Then, three classical effects of natural surfaces are classified: lotus effect, salvinia effect, and petal effect, and the promising strategies to fabricate biomimetic superhydrophobic materials are highlighted. Finally, the prospects and challenges of this area in the future are proposed.

Characterization of underwater stability of superhydrophobic surfaces using quartz crystal microresonators.

We synthesized porous aluminum oxide nanostructures directly on a quartz crystal microresonator and investigated the properties of superhydrophobic surfaces, including the surface wettability, water permeation, and underwater superhydrophobic stability. After increasing the pore diameter to 80 nm (AAO80), a gold film was deposited onto the AAO80 membrane, and the pore entrance size was reduced to 30 nm (AAO30). The surfaces of the AAO80 and AAO30 were made to be hydrophobic through chemical modification by incubation with octadecanethiol (ODT) or octadecyltrichlorosilane (OTS), which produced three different types of superhydrophobic surfaces on quartz microresonators: OTS-modified AAO80 (OTS-AAO80), ODT-modified AAO30 (ODT-AAO30), and ODT-OTS-modified AAO30 (TS-AAO30). The loading of a water droplet onto a microresonator or the immersion of a resonator into water induced changes in the resonance frequency that corresponded to the water permeation into the nanopores. TS-AAO30 exhibited the best performance, with a low degree of water permeation, and a high stability. These features were attributed to the presence of sealed air pockets and the narrow pore entrance diameter.

Controlling the Cassie-to-Wenzel Transition: an Easy Route towards the Realization of Tridimensional Arrays of Biological Objects

Abstract In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited as an effective micro-fabrication strategy to obtain highly ordered arrays of biological objects. To this purpose we fabricated a patterned surface wetted in the Cassie state, where we deposited a droplet containing genomic DNA. We observed that, when the droplet wets the surface in the Cassie state, an array of DNA filaments pinned on the top edges between pillars is formed. Conversely, when the Cassie-to-Wenzel transition occurs, DNA can be pinned at different height between pillars. These results open the way to the realization of tridimensional arrays of biological objects.

Controlling the Cassie-to-Wenzel Transition: an Easy Route towards the Realization of Tridimensional Arrays of Biological Objects

In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited as an effective micro-fabrication strategy to obtain highly ordered arrays of biological objects. To this purpose we fabricated a patterned surface wetted in the Cassie state, where we deposited a droplet containing genomic DNA. We observed that, when the droplet wets the surface in the Cassie state, an array of DNA filaments pinned on the top edges between pillars is formed. Conversely, when the Cassie-to-Wenzel transition occurs, DNA can be pinned at different height between pillars. These results open the way to the realization of tridimensional arrays of biological objects.

Perfluoropolyether-functionalized gas diffusion layers for proton exchange membrane fuel cells

Linear perfluoropolyether (PFPE) peroxide was used to confer superhydrophobic surface properties to gas diffusion layer (GDL) by means of direct functionalization of a GDL based on carbon cloth (CC) material. The thermal decomposition of a linear PFPE peroxide produces linear PFPE radicals that covalently bond the unsaturated moieties on the surface. Perfluorinated radicals are directly and covalently bound to the carbonaceous structure of the CC without any spacer that could decrease both thermal and chemical stability of the GDL. The obtained CC hydrophobicity exceeded the superhydrophobicity threshold and was enduringly stable. The relationship between the linkage of fluorinated chains and the variations of surface chemical–physical properties were studied combining X-ray photoelectron spectroscopy (XPS), resistivity measurements, scanning electron microscopy (SEM) and contact angle measurements. Despite the excellent insulating properties of the PFPE polymer, the functionalized carbonaceous materials substantially retained their conductive properties. The PFPE-modified GDLs were tested in a single fuel cell at the lab scale. The cell tests were run at two temperatures (60 °C and 80 °C) with a relative humidity (RH) of hydrogen and air feeding gases equal to 80/100% and 60/100%, respectively.

Controllable fabrication of periodic arrays of high-aspect-ratio micro-nano hierarchical structures and their superhydrophobicity

This paper demonstrates a flexible and controllable fabrication of vertically aligned and high-aspect-ratio (HAR) micro-nano hierarchical structures using conventional micro-technologies. We first masked the nanopatterns on a photoresist mold by shifting the same photomask, which could be performed using conventional contact microlithography. Thereby replicating nanopatterns onto an aluminium mold and successfully fabricating silicon nanopillar arrays about 300 nm in diameter and 5 µm in height via the deep reactive etching (DRIE) process. We also fabricated micro-nano hierarchical structures with variable aspect ratios using the proposed nanopattern technology and DRIE process without using any special nanopatterning equipment or techniques. The proposed method not only simplified the fabrication process but also produced HAR (higher than 15) structures. We also investigate the replica molding steps from the fabricated silicon stamp to a UV-curable polymer replica using a PDMS mold and conventional nano-imprinting, where each nanopillar diameter was 320 nm with 95% fidelity. As a result, the hierarchical structure arrays show stable superhydrophobic surface properties with a contact angle of approximately 160°. Owing to the cost efficiency of mass production and the fidelity of the strategy, the methodology could provide a general approach for fabricating complex three-dimensional periodic hierarchical structures onto a single chip and can be applied to various fields of multifunctional applications.

Fabrication and icing property of superhydrophilic and superhydrophobic aluminum surfaces derived from anodizing aluminum foil in a sodium chloride aqueous solution

An aluminum foil with a rough surface was first prepared by anodic treatment in a neutral aqueous solution with the help of pitting corrosion of chlorides. First, the hydrophobic Al surface (contact angle around 79°) became superhydrophilic (contact angle smaller than 5°) after the anodizing process. Secondly, the superhydrophilic Al surface became superhydrophobic (contact angle larger than 150°) after being modified by oleic acid. Finally, the icing property of superhydrophilic, untreated, and superhydrophobic Al foils were investigated in a refrigerated cabinet at −12°C. The mean total times to freeze a water droplet (6μL) on the three foils were 17s, 158s and 1604s, respectively. Thus, the superhydrophilic surface accelerates the icing process, while the superhydrophobic surface delays the process. The main reason for this transition might mainly result from the difference of the contact area of the water droplet with Al substrate: the increase in contact area with Al substrate will accelerate the heat conduct process, as well as the icing process; the decrease in contact area with Al substrate will delay the heat conduct process, as well as the icing process. Compared to the untreated Al foil, the contact area of the water droplet with the Al substrate was higher on superhydrophilic surface and smaller on the superhydrophobic surface, which led to the difference of the heat transfer time as well as the icing time.

Corrosion resistance properties of superhydrophobic copper surfaces fabricated by one-step electrochemical modification process

Superhydrophobic copper surfaces have been prepared by a one-step electrochemical modification process in an ethanolic stearic acid solution. In this work, the corrosion properties of hydrophobic copper surface and superhydrophobic copper surfaces were analyzed by means of electrochemical analyses and compared with that of as-received bare copper substrate. The decrease of corrosion current density (icorr) as well as the increase of polarization resistance (Rp) obtained from potentiodynamic polarization curves revealed that the superhydrophobic film on the copper surfaces improved the corrosion resistance performance of the copper substrate.

Fabrication of Superhydrophobic Conical Structures of Polysiloxane on Mg Plates Using an Immersion Process

Superhydrophobic surfaces have drawn the attention of the scientific and industrial communities alike owing to their immense potential to contribute to fundamental research and practical applications. Superhydrophobic surfaces can be used in self-cleaning, ice resistance, and applications in nano-/micro-fluidic devices. Many biological surfaces such as the lotus leaf, and the legs of a water spider are water repellent. Notably, the structure and chemical properties of a surface are the key factors that determine the superhydrophobicity of the surface of a material. For instance, the numerous papillae on the lotus leaf are coated with wax, which is a low surface energy material. The papillae on the lotus leaf and the conical structures on legs of the water spider are crucial in lending superhydrophobic properties to the surfaces. Nano-/micro-binary structures on surfaces trap air and dramatically reduce the contact area between the surface and the water droplet. Superhydrophobic surfaces have been conventionally fabricated by creating nano-scale hierarchical structures and by coating the surfaces with materials of low-surface-energies. Fluorinated alkyl silanes and long chain fatty acids are commonly used as lowsurface-energy materials. However, Cassie-Baxter's model demonstrated that rough surface structures are important to retain air, as they cushion water droplets. Provided that a large amount of air is retained on the surface, the surface can be expected to show superhydrophobic properties. Therefore, an appropriate conformation and morphology of the surface are crucial factors to realize superhydrophobic surface properties. Many techniques including etching, sol-gel methods, phase-separation methods, electro chemical deposition, electrospinning, and lithography have been used to create rough surfaces. Conical nano-/micro-binary structures on the surface have received considerable attention because of their geometry and physical properties. Conical surface structures have been fabricated using a variety of materials. For instance, conical nanocarbon structures have been fabricated on a transparent and flexible substrate using an ion irradiation technique at low temperatures. These structures were found to exhibit superior field emission properties as compared to carbon nanotubes. In another example, nickel surfaces containing nano-/micro conical arrays were produced by electrodeposition in the presence of ethylenediamine. The modified nickel surfaces exhibited superhydrophobicity without requiring modification with low surface energy materials. Further nanoconical arrays of glass have also been obtained using a chemical etching process. Even though nanoconical structures have gained considerable focus for various applications ranging from electronic devices to the fabrication of superhydrophobic surfaces, materials that can be used for assembling nanoconical structures are limited. In the present work, we report a simple method to fabricate superhydrophobic surfaces containing nanoconical structures on Mg plates using fluorinated alkyl triethoxysilane and 1,6-diphosphonohexane. This one-step process is simple and can be applied to large surfaces.

Design of multi-functional dual hole patterned carbon nanotube composites with superhydrophobicity and durability

Most current research on nanocomposites has focused on their bulk attributes, i.e., electrical, microwave, thermal, and mechanical properties. In practical applications, surface properties such as robustness against environmental contamination are critical design considerations if intrinsic properties are to be maintained. The aim of this research is to combine the bulk properties of nanocomposites with the superhydrophobic surface properties provided by imprinting techniques to create a single multi-functional system with enhanced bulk properties. We report the development of a highly conductive superhydrophobic nanotube composite, which is directly superimposed with a durable dual hole pattern through imprinting techniques. The dual hole pattern avoids the use of high slenderness ratio structures resulting in a surface which is robust against physical damage. Its stable superhydrophobic properties were characterized both theoretically and experimentally. By incorporating high aspect ratio carbon nanotubes (CNTs), the dual patterned composites can also be effectively used for anti-icing and deicing applications where their superhydrophobic surface suppresses ice formation and their quick electric heating response at low voltage eliminates remaining frost. In addition, superior electromagnetic interference (EMI) shielding effectiveness (SE) was attained, with one of the highest values ever reported in the literature. Open image in new window

Anti-Icing Property of the Prepared Super-Hydrophobic Octadecyltrichlorosilane (OTS) Film by Phase Separation Method

In this paper, we prepared an octadecyltrichlorosilane(OTS) super-hydrophobic film using phase separation method to demonstrate the anti-icing property of super-hydrophobic surfaces. We investigated the super-hydrophobicity of the surface in -5°C environment, as well as the icing process of water droplets on the surface which proceeded at the temperature low to -15°C. We found that the prepared OTS film retained its super-hydrophobicity in the -5°C environment by the measurement of contact angle. It was observed that the icing progress of water droplets on the super-hydrophobic surface was greatly retarded. Based on the classical heterogeneous nucleation theory, it concluded that the ice formation is directly related to the surface wettability. This research would be beneficial to the preparation of anti-icing films.