Superhydrophobic hierarchical surfaces fabricated by anodizing of oblique angle deposited Al-Nb alloy columnar films

A combined process of oblique angle magnetron sputtering and anodizing has been developed to tailor superhydrophobic surfaces with hierarchical morphology. Isolated submicron columns of single-phase Al-Nb alloys are deposited by magnetron sputtering at several oblique deposition angles on a scalloped substrate surface, with the gaps between columns increasing with an increase in the deposition angle from 70° to 110°. Then, the columnar films have been anodized in hot phosphate-glycerol electrolyte to form a nanoporous anodic oxide layer on each column. Such surfaces with submicron-/nano-porous structure have been coated with a fluoroalkyl phosphate layer to reduce the surface energy. The porous surface before coating is superhydrophilic with a contact angle for water is less than 10°, while after coating the contact angles are larger than 150°, being superhydrophobic. The beneficial effect of dual-scale porosity to enhance the water repellency is found from the comparison of the contact angles of the submicron columnar films with and without nanoporous oxide layers. The larger submicron gaps between columns are also preferable to increase the water repellency.     

A simple fabrication method for mechanically robust superhydrophobic surface by hierarchical aluminum hydroxide structures

Superhydrophobic surfaces with uniformly superhydrophobic surface where nano-scale structures were fabricated by alkali surface modification method and self-assembled monolayer coating. To enhance mechanical durability of the superhydrophobicity, we propose the fabrication process for dual-scale hierarchical structures combining both microstructure via sandblasting techniques and the nanostructured aluminum hydroxide layer. The superhydrophobic surfaces fabricated by both methods exhibited a high water contact angle and very low contact angle hysteresis. By forming the hierarchical structure, the mechanical durability of superhydrophobic aluminum hydroxide surface was improved. The resulting hierarchical structures are suitable for diverse applications of aluminum in various industrial areas, including self-cleaning, anti-frosting, and microfluidic devices for rigorous environments.     

Superhydrophobic surfaces via controlling the morphology of ZnO micro/nano complex structure

ZnO micro/nano complex structure films, including reticulate papillary nodes, petal-like and flake-hole, have been self-assembled by a hydrothermal technique at different temperatures without metal catalysts. The wettability of the above film surfaces was modified with a simple coating of heptadecafluorodecyltrimethoxy-silane in toluene. After modifying, the surface of ZnO film grown at 50~${^\circ}$C was converted from superhydrophilic with a water contact angle lower than 5$^{\circ}$ to superhydrophobic with a water contact angle of 165$^{\circ}$. Additionally, the surface of reticulate papillary nodes ZnO film grown at 100~${^\circ}$C had excellent superhydrophobicity, with a water contact angle of 173$^{\circ}$ and a sliding angle lower than 2$^{\circ}$. Furthermore, the water contact angle on the surface of petal-like and flake-hole ZnO films grown at 150~${^\circ}$C and 200~${^\circ}$C were found to be 140$^{\circ}$ and 120$^{\circ}$, respectively. The wettability for the samples was found to depend strongly on the surface morphology which results from the growth temperature.     

Preparation of hybrid film with superhydrophobic surfaces based on irregularly structure by emulsion polymerization

A superhydrophobic surface originated from quincunx-shape composite particles was obtained by utilizing the encapsulation and graft of silica particles to control the surface chemistry and morphology of the hybrid film. The composite particles make the surface of film form a composite interface with irregular binary structure to trap air between the substrate surface and the liquid droplets which plays an essential role in obtaining high water contact angle and low water contact angle hysteresis. The water contact angle on the hybrid film is determined to be 154 ± 2° and the contact angle hysteresis is less than 5°. This is expected to be a simple and practical method for preparing self-cleaning hydrophobic surfaces on large area.     

Fluorination of polymethylmethaacrylate with tetrafluoroethane using DC glow discharge plasma

Fluorination of polymer surfaces has technological applications in various fields such as microelectronics, biomaterials, textile, packing, etc. In this study PMMA surfaces were fluorinated using DC glow discharge plasma. Tetrafluoroethane was used as the fluorinating agent. On the fluorinated PMMA surface, static water contact angle, surface energy, optical transmittance (UV-vis), XPS and AFM analyses were carried out. After the fluorination PMMA surface becomes hydrophobic with water contact angle of 107° without losing optical transparency. Surface energy of fluorine plasma-treated PMMA decreased from 35 mJ/cm² to 21.2 mJ/cm². RMS roughness of the fluorinated surface was 4.01 nm and XPS studies revealed the formation of C-CF_x and CF₃ groups on the PMMA surface.     

Controlling the micro/nanostructure of self-cleaning polymer coating

Polypropylene bio-mimic self-cleaning surfaces with porous micro-nano-binary morphology structures were prepared by a simple casting method. The influence of the cooling process and solvent composition on water contact angle, sliding angles and self-cleaning properties has been investigated. Detailed SEM morphology studies revealed that the polymer used in this work is commercial-grade granular low-density polyethylene (LDPE) forms petal-like crystalline, which are of micrometer scale in length and nanometer scale in thickness. The nano-crystallines on the surface represent a porous three-dimensional micro-nano-binary structure. It was found that a compromise to the film porosity and crystal nano structure is essential for achieving a satisfied self-cleaning surface. Under optimum condition, a water contact angle of 152.2°, and a sliding angle of 1.7° can be obtained using this simple method.     

Effect of plasma pretreatment on adhesion and mechanical properties of UV-curable coatings on plastics

An attempt was made to study the effect of plasma surface activation on the adhesion of UV-curable sol-gel coatings on polycarbonate (PC) and polymethylmethacrylate (PMMA) substrates. The sol was synthesized by the hydrolysis and condensation of a UV-curable silane in combination with Zr-n-propoxide. Coatings deposited by dip coating were cured using UV-radiation followed by thermal curing between 80 °C and 130 °C. The effect of plasma surface treatment on the wettability of the polymer surface prior to coating deposition was followed up by measuring the water contact angle. The water contact angle on the surface of as-cleaned substrates was 80° ± 2° and that after plasma treatment was 43° ± 1° and 50° ± 2° for PC and PMMA respectively. Adhesion as well as mechanical properties like scratch resistance and taber abrasion resistance were evaluated for coatings deposited over plasma treated and untreated surfaces.     

Superhydrophobic wind turbine blade surfaces obtained by a simple deposition of silica nanoparticles embedded in epoxy

Samples of wind turbine blade surface have been covered with a superhydrophobic coating made of silica nanoparticles embedded in commercial epoxy paint. The superhydrophobic surfaces have a water contact angle around 152°, a hysteresis less than 2° and a water drop sliding angle around 0.5°. These surfaces are water repellent so that water drops cannot remain motionless on the surface. Examination of coated and uncoated surfaces with scanning electron microscopy and atomic force microscopy, together with measurements of water contact angles, indicates that the air trapped in the cavity enhances the water repellency similarly to the lotus leaf effect. Moreover, this new coating is stable under UVC irradiation and water pouring. The production of this nanoscale coating film being simple and low cost, it can be considered as a suitable candidate for water protection of different outdoor structures.     

Molecular dynamics simulation of wetting on modified amorphous silica surface

The microscopic wetting of water on amorphous silica surfaces has been investigated by molecular dynamics simulation. Different degrees of surface hydroxylation/silanization were considered. It was observed that the hydrophobicity becomes enhanced with an increase in the degree of surface silanization. A continuous transformation from hydrophilicity to hydrophobicity can be attained for the amorphous silica surfaces through surface modification. From the simulation result, the contact angle can exceed 90° when surface silanization percentage is above 50%, showing a hydrophobic character. It is also found that when the percentage of surface silanization is above 70% on the amorphous silica surface, the water contact angle almost remains unchanged (110–120°). This phenomenon is a little different from the wetting behavior on smooth quartz plates in previous experimental report. This change in the wettability on modified amorphous silica surfaces can be interpreted in terms of the interaction between water molecules and the silica surfaces.     

Easy fabrication of large-size superhydrophobic surfaces by atmospheric pressure plasma polymerization with non-polar aromatic hydrocarbon in an in-line process

We report on the formation of superhydrophobic surfaces on glass by plasma polymerization with non-polar aromatic hydrocarbon, at atmospheric pressure, in an in-line process. The glass was simply treated by radio frequency (RF) plasma with a mixture of toluene and hexamethyldisiloxane (HMDSO). The hydrophobicity of the sample surfaces increase with increasing plasma treatments; contact angles of 150° for water droplets are achieved. It is attributed mainly to its high content of non-polar hydrophobic phenyl groups and its rough surface.     

Laser microstructuring for fabricating superhydrophobic polymeric surfaces

In this paper we show the fabrication of hydrophobic polymeric surfaces through laser microstructuring. By using 70-ps pulses from a Q-switched and mode-locked Nd:YAG laser at 532 nm, we were able to produce grooves with different width and separation, resulting in square-shaped pillar patterns. We investigate the dependence of the morphology on the surface static contact angle for water, showing that it is in agreement with the Cassie-Baxter model. We demonstrate the fabrication of a superhydrophobic polymeric surface, presenting a water contact angle of 157°. The surface structuring method presented here seems to be an interesting option to control the wetting properties of polymeric surfaces.     

Fabrication and wear protection performance of superhydrophobic surface on zinc

A simple two-step process has been developed to render zinc surface superhydrophobic, resulting in low friction coefficient and long wear resistance performance. The ZnO film with uniform and packed nanorod structure was firstly created by immersing the zinc substrates into 4% N,N-dimethylformamide solution. The as-fabricated surface was then coated a layer of fluoroalkylsilane (FAS) by gas phase deposition. Scanning electron microscopy (SEM) and water contact angle (WCA) measurement have been performed to characterize the morphological feature, chemical composition and superhydrophobicity of the surface. The resulting surfaces have a WCA as high as 156° and provide effective friction-reducing and wear protection for zinc substrate.     

Formation of a high hydrophilic/hydrophobic contrast surface on PET substrates by ECR generated sulfur hexafluoride plasma

High hydrophilic/hydrophobic contrast surfaces on polyethylene terephthalate (PET) substrates were formed by shadow mask technique in electron cyclotron resonance generated sulfur hexafluoride plasma atmosphere. The X-ray photoelectron spectroscopy (XPS) analyses indicate that the unmasked PET surfaces contained a high proportion of the CF₂-CF₂ groups, and therefore were hydrophobic with large water contact angle. However, the surface wettability was found to increase drastically on the masked PET surfaces. This could be resulted from a mass of COF (acid fluoride) compounds observed by XPS on the masked film surfaces. The COF compounds could react with atmospheric moisture to form -COOH groups, which in turn increased the surface wettability. In addition, the surface wetting property of the masked areas was found to change significantly with the plasma treatment time, the mask-to-substrate distance and the storage time after the treatment. The best contract in water contact angle obtained from the treated PET samples was larger than 100° after 168 h of storage.     

Wetting and superhydrophobic properties of PECVD grown hydrocarbon and fluorinated-hydrocarbon coatings

Wetting characteristics of micro-nanorough substrates of aluminum and smooth silicon substrates have been studied and compared by depositing hydrocarbon and fluorinated-hydrocarbon coatings via plasma enhanced chemical vapor deposition (PECVD) technique using a mixture of Ar, CH₄ and C₂F₆ gases. The water contact angles on the hydrocarbon and fluorinated-hydrocarbon coatings deposited on silicon substrates were found to be 72° and 105°, respectively. However, the micro-nanorough aluminum substrates demonstrated superhydrophobic properties upon coatings with fluorinated-hydrocarbon providing a water contact angle of ∼165° and contact angle hysteresis below 2° with water drops rolling off from those surfaces while the same substrates showed contact angle of 135° with water drops sticking on those surfaces. The superhydrophobic properties is due to the high fluorine content in the fluorinated-hydrocarbon coatings of ∼36 at.%, as investigated by X-ray photoelectron spectroscopy (XPS), by lowering the surface energy of the micro-nanorough aluminum substrates.     

Residual stress induced wetting variation on electric brush-plated Cu film

Nanocrystalline Cu film with a mirror surface finishing is prepared by the electric brush-plating technique. The as- prepared Cu film exhibits a superhydrophilic behavior with an apparent water contact angle smaller than 10°. A subsequent increase in the water contact angle and a final wetting transition from inherent hydrophilicity with water contact angle smaller than 90° to apparent hydrophobicity with water contact angle larger than 90° are observed when the Cu film is subjected to natural aging. Analysis based on the measurement of hardness with nanoindentation and the theory of the bond-order-length-strength correlation reveals that this wetting variation on the Cu film is attributed to the relaxation of residual stress generated during brush-plating deposition and a surface hydrophobization role associated with the broken bond polarization induced by surface nanostructure.     

Surface structures and osteoblast response of hydrothermally produced CaTiO3 thin film on Ti-13Nb-13Zr alloy

This study investigated the surface characteristics and in vitro biocompatibility of a titanium (Ti) oxide layer incorporating calcium ions (Ca) obtained by hydrothermal treatment with or without post heat-treatment in the Ti-13Nb-13Zr alloy. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. In vitro biocompatibility of the Ca-containing surfaces was assessed in comparison with untreated surfaces using a pre-osteoblast cell line. Hydrothermal treatment produced a crystalline CaTiO₃ layer. Post heat-treatment at 400 °C for 2 h in air significantly decreased water contact angles in the CaTiO₃ layer (p < 0.001). The Ca-incorporated alloy surfaces displayed markedly increased cell viability and ALP activity compared with untreated surfaces (p < 0.001), and also an upregulated expression of various integrin genes (α1, α2, α5, αv, β1 and β3) at an early incubation time-point. Post heat-treatment further increased attachment and ALP activity in cells grown on Ca-incorporated Ti-13Nb-13Zr alloy surfaces. The results indicate that the Ca-incorporated oxide layer produced by hydrothermal treatment and a simple post heat-treatment may be effective in improving bone healing in Ti-13Nb-13Zr alloy implants by enhancing the viability and differentiation of osteoblastic cells.     

Plasma treatment of ITO surfaces to improve luminescence characteristics of organic light-emitting devices with dopants

Indium-tin-oxide (ITO) surfaces were treated with O₂ and H₂ plasmas. The contact angle of water, X-ray photoelectron spectroscopy (XPS) spectra, and luminescence characteristics of organic light-emitting devices (OLEDs) fabricated on plasma-treated ITO surfaces using poly(N-vinylcarbazole) (PVK) films doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) or Nile Red were investigated.Using O₂ plasma treatment, the contact angle was reduced from 35° to 13°. The luminance of OLEDs with rubrene was significantly improved. The luminous color of an OLED inserted poly (3,4-ethylenedioxythiophene)-polystyrene sulphonic acid (PEDOT-PSS) layer between Nile Red-doped PVK film and O₂-plasma-treated ITO surface turned white as the applied voltage increased.     

Micropatterning of perfluoroalkyl self-assembled monolayers for arraying proteins and cells on chips

Organosilane self-assembled monolayers (SAMs) with perfluoroalkyl groups (R_f) on glass surfaces were used for arraying proteins and cells on chips. Quartz crystal microbalance measurements confirmed the inhibition of protein adsorption on R_f-SAM-modified surfaces and showed efficient adsorption on hydroxyl-, carboxyl-, and amino group-modified surfaces. The characteristics of R_f-modified surfaces were evaluated using solvent contact angle measurement and Fourier transform infrared (FTIR) spectroscopy. The R_f surface was highly water- and oil-resistant, as inferred from the contact angles of water, oleic acid, and hexadecane. Specific peaks of IR spectra were detected in the region from 1160 to 1360 cm⁻¹. Etching with dry plasma completely exfoliated the R_f-SAM, exposing the underlying intact glass surface. Modification conditions were optimized using contact angle and FTIR measurements. After dry plasma processing, the contact angles of all solvents became undetectable, and the IR peaks disappeared. Micrometer scale protein and cell patterns can be fabricated using the proposed method. Protein adsorption on micropatterned R_f-SAM-modified chips was evaluated using fluorescence analysis; protein adsorption was easily controlled by patterning R_f-SAM. PC12 and HeLa cells grew well on micropatterned R_f-SAM-modified chips. Micropatterning of R_f-SAM by dry plasma treatment with photolithography is useful for the spatial arrangement of proteins and cells.     

Water condensation on zinc surfaces treated by chemical bath deposition

Water condensation, a complex and challenging process, is investigated on a metallic (Zn) surface, regularly used as anticorrosive surface. The Zn surface is coated with hydroxide zinc carbonate by chemical bath deposition, a very simple, low-cost and easily applicable process. As the deposition time increases, the surface roughness augments and the contact angle with water can be varied from 75° to 150°, corresponding to changing the surface properties from hydrophobic to ultrahydrophobic and superhydrophobic. During the condensation process, the droplet growth laws and surface coverage are found similar to what is found on smooth surfaces, with a transition from Cassie-Baxter to Wenzel wetting states at long times. In particular, it is noticeable in view of corrosion effects that the water surface coverage remains on order of 55%.     

基于热致相分离法和机械撕除技术的可再生超疏水表面构建

We report a simple preparation method of a renewable superhydrophobic surface by ther-mally induced phase separation (TIPS) and mechanical peeling. Porous polyvinylidene fluo-ride (PVDF) membranes with hierarchical structures were prepared by a TIPS process under different cooling conditions, which were confirmed by scanning electron microscopy and mer-cury intrusion porosimetry. After peeling off the top layer, rough structures with hundreds of nanometers to several microns were obtained. A digital microscopy determines that the surface roughness of peeled PVDF membranes is much higher than that of the original PVDF membrane, which is important to obtain the superhydrophobicity. Water contact angle and sliding angle measurements demonstrate that the peeled membrane surfaces display super-hydrophobicity with a high contact angle (152°) and a low sliding angle (7.2°). Moreover, the superhydrophobicity can be easily recovered for many times by a simple mechanical peel-ing, identical to the original superhydrophobicity. This simple preparation method is low cost, and suitable for large-scale industrialization, which may offer more opportunities for practical applications.