Superhydrophobic nanostructured silicon surfaces with controllable broadband reflectance

Nanostructured superhydrophobic silicon surfaces with tunable reflectance are fabricated via a simple maskless deep reactive-ion etching process. By controlling the scale of the high-aspect-ratio nanostructures on a wafer-scale surface, surface reflectance is maximized or minimized over the UV-vis-IR range while maintaining superhydrophobic properties.     

Electrophoretic deposition of unstable colloidal suspensions for superhydrophobic surfaces

A novel method to fabricate superhydrophobic surfaces using electrophoretic deposition (EPD) is presented. EPD presents a readily scalable, customizable, and potentially low cost surface manufacturing process. Low surface energy materials with high surface roughness are achieved using EPD of unstable hydrophobic SiO(2) particle suspensions. The effect of suspension stability on surface roughness is quantitatively explored with optical absorbance measurements (to determine suspension stability) and atomic force microscopy (to measure surface roughness). Varying suspension pH modulates suspension stability. Contrary to most applications of EPD, we show that superhydrophobic surfaces favor mildly unstable suspensions since they result in high surface roughness. Particle agglomerates formed in unstable suspensions lead to highly irregular films after EPD. After only 1 min of EPD, we obtain surfaces with low contact angle hysteresis and static contact angles exceeding 160°. We also present a technique to enhance the mechanical durability of the superhydrophobic surfaces by adding a polymeric binder to the suspension prior to EPD.     

Mimicking natural superhydrophobic surfaces and grasping the wetting process: a review on recent progress in preparing superhydrophobic surfaces

A typical superhydrophobic (ultrahydrophobic) surface can repel water droplets from wetting itself, and the contact angle of a water droplet resting on a superhydrophobic surface is greater than 150°, which means extremely low wettability is achievable on superhydrophobic surfaces. Many superhydrophobic surfaces (both manmade and natural) normally exhibit micro- or nanosized roughness as well as hierarchical structure, which somehow can influence the surface's water repellence. As the research into superhydrophobic surfaces goes deeper and wider, it is becoming more important to both academic fields and industrial applications. In this work, the most recent progress in preparing manmade superhydrophobic surfaces through a variety of methodologies, particularly within the past several years, and the fundamental theories of wetting phenomena related to superhydrophobic surfaces are reviewed. We also discuss the perspective of natural superhydrophobic surfaces utilized as mimicking models. The discussion focuses on how the superhydrophobic property is promoted on solid surfaces and emphasizes the effect of surface roughness and structure in particular. This review aims to enable researchers to perceive the inner principles of wetting phenomena and employ suitable methods for creation and modification of superhydrophobic surfaces.     

Superhydrophilic/superhydrophobic surfaces fabricated by spark‐coating

In this study, the authors researched the preparations of superhydrophilic/superhydrophobic surfaces on commercial cup stock polyethylene coated papers by using sparked aluminum nanoparticles deposited on substrates through a sparking process. In this stage, the surface was porous and showed superhydrophilic properties. The samples were then annealed in air at various temperatures and some transformed to superhydrophobicity. It is well known that a suitable roughness in combination with low surface energy has been required to obtain superhydrophobic surfaces. Therefore, it is believed that during annealing process, when polyethylene is diffused from the substrate through the nanoparticle films and the superhydrophobic characteristics were created. The scanning electron microscope images showed that the film surfaces had a fluffy structure for both the as‐deposited and the annealed samples. However, the atomic force microscopy phase images showed completely different surface properties. Moreover, the X‐ray photoelectron spectroscopy spectra showed different surface chemical compositions. The experimental results revealed that the working temperature to produce superhydrophobic surfaces depended on the sparked film thickness. Furthermore, in order to prove the assumption explained above, glass and poly (methyl methacrylate) were also used as substrates.     

高黏附性超疏水表面的研究进展

黏附性是超疏水表面的一个重要特性,随着对超疏水表面研究的深入,具有响应特性的智能超疏水表面引起了人们的极大兴趣,而能够作为“机械手”抓取液滴的具有高黏附性的超疏水表面自然成为关注对象。 本文讨论了表面形貌和表面化学组成对超疏水表面黏附性的影响,综述了近年来高黏附性超疏水表面制备方面的研究进展,并对高黏附性超疏水表面未来的研究方向做出了展望。     

Superhydrophobic surfaces using selected zinc oxide microrod growth on ink-jetted patterns

The synthesis and properties of superhydrophobic surfaces based on binary surface topography made of zinc oxide (ZnO) microrod-decorated micropatterns are reported. ZnO is intrinsically hydrophilic but can be utilized to create hydrophobic surfaces by creating artificial roughness via microstructuring. Micron scale patterns consisting of nanocrystalline ZnO seed particles were applied to glass substrates with a modified ink-jet printer. Microrods were then grown on the patterns by a hydrothermal process without any further chemical modification. Water contact angle (WCA)(1) up to 153° was achieved. Different micro array patterned surfaces with varying response of static contact angle or sessile droplet analysis are reported.     

超疏水性表面的制备及应用进展

近年来,受荷叶、水黾腿、壁虎脚等天然超疏水生物表面特性的启发,研究者们进行了大量仿生超疏水表面材料的制备及应用研究。超疏水性表面因其特殊的微纳分层结构,具有自清洁、防覆冰、防腐蚀、减阻等优异性能。本文阐述了表面润湿、疏水的基本机理,以及超疏水表面研究的理论基础,对超疏水表面制备的最新研究进展进行了综述,并揭示了研究中存在的问题。最后,介绍了超疏水表面在涂料、织物、防腐、抗菌及防雾等领域中的应用,展望了其未来的研究方向和前景。     

Superhydrophobic surfaces from surface-hydrophobized cellulose fibers with stearoyl groups

In this report, surface-hydrophobized cellulose fibers by stearoyl groups were used for the construction of superhydrophobic surfaces. The product after the synthesis contains two components: cellulose microfibers as the major component and nanoscaled segments in small amounts. The crystalline structure of cellulose was maintained after surface modification based on solid-state ¹³C NMR spectroscopy. Superhydrophobic surfaces showing static water contact angles of >150° were fabricated using freshly prepared products containing both components via the facile route, e.g., solvent casting. The cellulose types, microcrystalline cellulose or cotton linter cellulose fibers, did not significantly affect the chemical modification of cellulose fibers, but the superhydrophobic surfaces using surface-hydrophobized cotton linters as starting materials exhibited higher surface hydrophobicity and better impact stability in comparison to shorter microcrystalline cellulose. Due to the presence of a crystalline cellulose skeleton, the obtained superhydrophobic surfaces are stable during the heat treatment at 80 °C.     

Nano-scale superhydrophobicity: suppression of protein adsorption and promotion of flow-induced detachment

Wall adsorption is a common problem in microfluidic devices, particularly when proteins are used. Here we show how superhydrophobic surfaces can be used to reduce protein adsorption and to promote desorption. Hydrophobic surfaces, both smooth and having high surface roughness of varying length scales (to generate superhydrophobicity), were incubated in protein solution. The samples were then exposed to flow shear in a device designed to simulate a microfluidic environment. Results show that a similar amount of protein adsorbed onto smooth and nanometer-scale rough surfaces, although a greater amount was found to adsorb onto superhydrophobic surfaces with micrometer scale roughness. Exposure to flow shear removed a considerably larger proportion of adsorbed protein from the superhydrophobic surfaces than from the smooth ones, with almost all of the protein being removed from some nanoscale surfaces. This type of surface may therefore be useful in environments, such as microfluidics, where protein sticking is a problem and fluid flow is present. Possible mechanisms that explain the behaviour are discussed, including decreased contact between protein and surface and greater shear stress due to interfacial slip between the superhydrophobic surface and the liquid.     

A nonlithographic top-down electrochemical approach for creating hierarchical (micro-nano) superhydrophobic silicon surfaces

Superhydrophobic surfaces are biomimetic structures with potential applications in several key technological areas. In the past decade, several top-down and bottom-up fabrication methods have been developed to create such surfaces. These typically combine a hierarchical structure and low surface energy coatings to increase the contact angle and decrease the rolling angles. Silicon-based superhydrophobic surfaces are particularly attractive since they can be integrated with active electronics in order to protect them from the detrimental effects of environmental water and moisture. In this work, we introduce a simple and inexpensive process incorporating electrochemical surface modification (to create a fractal shape micro-nano topography) in combination with a final wet etching step to fabricate a superhydrophobic silicon surface with a contact angle of 160 degrees and a sliding angle of less than 1 degree.     

Literature review on superhydrophobic self‐cleaning surfaces produced by electrospinning

Self‐cleaning surface is potentially a very useful addition for many commercial products due to economic, aesthetic, and environmental reasons. Super‐hydrophobic self‐cleaning, also called Lotus effect, utilizes right combination of surface chemistry and roughness to force water droplets to form high contact angle on a surface, easily roll off a surface and pick up dirt particles on its way. Electrospinning is a promising technique for creation of superhydrophobic self‐cleaning surfaces owing to a wide set of parameters that allow effectively controlling roughness of resulted webs. This article gives a brief introduction to the theory of super‐hydrophobic self‐cleaning and basic principles of the electrospinning process and reviews the scientific literature where electrospinning was used to create superhydrophobic surfaces. The article reviewed are categorized into several groups and their results are compared in terms of superhydrophobic properties. Several issues with current state of the art and highlights of important areas for future research are discussed in the conclusion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Formation of superhydrophobic surfaces by biomimetic silicification and fluorination

The amazing water repellency of many biological surfaces, exemplified by lotus leaves, has recently received a great deal of interest. These surfaces, called superhydrophobic surfaces, exhibit water contact angles larger than 150 degrees and a low contact angle hysteresis because of both their low surface energy and heterogeneously rough structures. In this paper, we suggest a biomimetic method, "biosilicification", for generating heterogeneously rough structures and fabricating superhydrophobic surfaces. The superhydrophobic surface was prepared by a combination of the formation of heterogeneously rough, nanosphere-like silica structures through biosilicification and the formation of self-assembled monolayers of fluorosilane on the surface. The resulting surface exhibited the water contact angle of 160.1 degrees and the very low water contact angle hysteresis of only 2.3 degrees, which are definite characteristics of superhydrophobic surfaces. The superhydrophobic property of our system probably resulted from the air trapped in the rough surface. The wetting behavior on the surface was in the heterogeneous regime, which was totally supported by Cassie-Baxter equation.     

Hydrocarbon versus fluorocarbon in the electrodeposition of superhydrophobic polymer films

To elaborate on superhydrophobic surfaces, we report the electrochemical synthesis, surface morphology, and wettability of hydrocarbon conductive polymer films obtained by the electrodeposition of polythiophene, poly(3,4-ethylenedioxythiophene) (i.e., PEDOT), and poly(3,4-ethylenedioxypyrrole) (i.e., PEDOP) derivatives. Highly hydrophobic films were obtained from n-C(14)H(29) and n-C(8)H(17) chains in the cases of polythiophenes and PEDOP, respectively. By contrast, superhydrophobic films were formed by the deposition of PEDOT substituted with n-C(10)H(21) chains (PEDOT-methyl undecanoate): static contact angle ≈ 160.6°, hysteresis ≈ 2°, and sliding angle ≈ 3°. Their surface properties were compared to those of previously reported fluorinated analogues. The water-repellent properties of PEDOT-methyl undecanoate were similar to the best surface properties obtained with fluorinated monomers. Even if the main approach for the chemical factor to build up superhydrophobic surfaces is via a coating of a fluorinated compound, this work confirms that the formation of fractal surfaces is able to achieve super-anti-wetting properties within a hydrocarbon series (less expensive with a favorable ecotoxic approach), and it opens a new path to bioinspired surfaces.     

Solvothermal synthesis of nanoporous polymer chalk for painting superhydrophobic surfaces

Reported here is a facile synthesis of nanoporous polymer chalk for painting superhydrophobic surfaces. Taking this nanoporous polymer as a media, superhydrophobicity is rapidly imparted onto three typical kinds of substrates, including paper, transparent polydimethylsiloxane (PDMS), and finger skin. Quantitative characterization showed that the adhesion between the water droplet and polymer-coated substrates decreased significantly compared to that on the original surface, further indicating the effective wetting mode transformation. The nanoporous polymer coating would open a new door for facile, rapid, safe, and larger scale fabrication of superhydrophobic surfaces on general substrates.     

Recent Advances in Dual-Function Superhydrophobic Antibacterial Surfaces

Bacterial adhesion and subsequent biofilm formation on the surfaces of synthetic materials imposes a significant burden in various fields, which can lead to infections in patients or reduce the service life of industrial devices. Therefore, there is increasing interest in imbuing surfaces with antibacterial properties. Bioinspired superhydrophobic surfaces with high water contact angles (>150°) exhibit excellent surface repellency against contaminations, thereby preventing initial bacterial adhesion and inhibiting biofilm formation. However, conventional superhydrophobic surfaces typically lack long-term durability and are incapable of achieving persistent efficacy against bacterial adhesion. To overcome these limitations, in recent decades, dual-function superhydrophobic antibacterial surfaces with both bacteria-repelling and bacteria-killing properties have been developed by introducing bactericidal components. These surfaces have demonstrated improved long-term antibacterial performance in addressing the issues associated with surface-attached bacteria. This review summarizes the recent advancements of these dual-function superhydrophobic antibacterial surfaces. First, a brief overview of the fabrication strategies and bacteria-repelling mechanism of superhydrophobic surfaces is provided and then the dual-function superhydrophobic antibacterial surfaces are classified into three types based on the bacteria-killing mechanism: i) mechanotherapy, ii) chemotherapy, and iii) phototherapy. Finally, the limitations and challenges of current research are discussed and future perspectives in this promising area are proposed.     

Design and fabrication of micro-textures for inducing a superhydrophobic behavior on hydrophilic materials

Artificial superhydrophobic surfaces are typically fabricated by tuning the surface roughness of intrinsically hydrophobic surfaces. We report here the design and fabrication of micro-textures for inducing a superhydrophobic behavior on hydrogen-terminated Si surfaces with an intrinsic water contact angle of approximately 74 degrees . The micro-textures consist of overhang structures with well-defined geometries fabricated by microfabrication technologies, which provide positions to support the liquid and prevent the liquid from entering into the indents between the micro-textures. As a result, water is in contact with a composite surface of solid and air, which induces the observed macroscopic superhydrophobic behavior.     

Preparation of a superhydrophobic rough surface

The relationship between the contact angles, surface tension, and surface roughness is reviewed. Numerical formulas related to the superhydrophobic rough surfaces of polymers are predicted with two approaches, the Wenzel and Cassie–Baxter models. With these models as a guide, an artificial superhydrophobic surface is created. Rough nylon surfaces mimicking the lotus leaf are created by the coating of a polyester surface with nylon‐6,6 short fibers via the flocking process. Poly(acrylic acid) chains aregrafted onto nylon‐6,6 surfaces, and this is followed by the grafting of 1H,1H‐perfluorooctylamine onto the poly(acrylic acid) chains. Water contact angles as high as 178° are achieved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 253–261, 2007.     

具有微纳米结构超疏水表面润湿性的研究

本文综述了近年来具有微纳米结构超疏水表面的研究进展。介绍了具有微纳米结构超疏水表面的制备方法，表面结构对超疏水性能的影响，周期性结构表面超疏水的条件，超疏水表面接触角滞后以及功能化超疏水表面等方面的研究，探讨了这一领域存在的问题及可能的发展方向。     

UV and thermally stable superhydrophobic coatings from sol-gel processing

A method for the preparation of inorganic superhydrophobic silica coatings using sol-gel processing with tetramethoxysilane and isobutyltrimethoxysilane as precursors is described. Incorporation of isobutyltrimethoxysilane into silica layers resulted in the existence of hydrophobic isobutyl surface groups, thereby generating surface hydrophobicity. When combined with the surface roughness that resulted from sol-gel processing, a superhydrophobic surface was achieved. This surface showed improved UV and thermal stability compared to superhydrophobic surfaces generated from polybutadiene by plasma etching. Under prolonged UV tests (ASTM D 4329), these surfaces gradually lost superhydrophobic character. However, when the as-prepared superhydrophobic surface was treated at 500 degrees C to remove the organic moieties and covered with a fluoroalkyl layer by a perfluorooctylsilane treatment, the surface regained superhydrophobicity. The UV and thermal stability of these surfaces was maintained upon exposure to temperatures up to 400 degrees C and UV testing times of 5500 h. Contact angles remained >160 degrees with contact angle hysteresis approximately 2 degrees.