Superhydrophobic polytetrafluoroethylene thin films with hierarchical roughness deposited using a single step vapor phase technique (original) (raw)
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Applied Surface Science, 2011
A series of superhydrophobic polytetrafluoroethylene (PTFE) surfaces were prepared by a facile cold pressing and sintering method, and their microstructures and wetting behaviors could be artificially tailored by altering sintering temperature and using different masks. Specifically, the microstructures mainly depended on the sintering temperature, whereas the wetting behaviors, water contact angle (WCA) and sliding angle (SA), greatly hinged on both the sintering temperature and mask. Then a preferable superhydrophobic surface with WCA of 162 ± 2 • and SA of 7 • could be obtained when the sintering temperature was 360 • C and the 1000 grit abrasive paper was used as a mask. In addition, it was worth noting that the as-prepared surfaces exhibited excellent stability under UV illumination, which was the most key factor for them toward practical applications.
Tuneable rough surfaces: A new approach for elaboration of superhydrophobic films
Surface Science, 2005
The present paper describes the process enabling the production of superhydrophobic surfaces by tailoring their surface topography and chemical properties. These surfaces have been developed using a simple plasma based techniques combining plasma etching and plasma polymerization on silicon substrates. These techniques have been chosen because they provide features such as large area processing and high reproducibility. The key step of this process is the modification of the surface topography of the substrate to create high roughness before deposition of fluorocarbon coating. The roughness on silicon wafer is induced by the over-etching of a photoresist layer by a SF6 plasma treatment. The different layers obtained exhibit contact angles from 102° up to 180° depending of the preparation conditions. The observations of the topology by scanning electron microscopy reveal that the presence of dendrites on the surface of the substrate favors the superhydrophobicity of the films. The variations of the contact angle have been explained using the Wenzel’s or Cassie’s models.
Preparation of large-scale, durable, superhydrophobic PTFE films using rough glass templates
Surface and Interface Analysis, 2017
Large superhydrophobic polytetrafluoroethylene (PTFE) films, with good durability, were successfully prepared by a facile, low cost, environmentally friendly templating method, using a PTFE emulsion. For the first time, commercially available rough glass was employed as a reusable template. The results show that both the microstructure of the glass template and the concentration of the PTFE emulsion play important roles in the superhydrophobicity of the films. Commercially available, acid-etched, rough glass is found to be an ideal template for such films, the superhydrophobicity increasing with decreasing emulsion concentration. Abrasive wear testing shows that superhydrophobic PTFE film, prepared under an optimal concentration of 5 wt% PTFE emulsion, has good abrasion resistance. Moreover, the results show that this method is suitable for the large-scale preparation of superhydrophobic PTFE films.
Applied Physics Letters, 2009
We have studied the effect of substrate roughness on the wettability and the apparent surface free energy ͑SFE͒ of sputter deposited polytetrafluoroethylene ͑PTFE͒ coatings deposited on untreated glass ͑average roughness, R a = 2.0 nm͒, plasma etched glass ͑R a = 7.4 nm͒, and sandblasted glass ͑R a = 4500 nm͒ substrates. The wettability of the PTFE coatings deposited on substrates with varying roughnesses was evaluated by measuring the apparent contact angle ͑CA͒ using a series of probe liquids from nonpolar aprotic to polar protic. The wettability measurements indicate that an apparent water CA of 152°with a sliding angle of 8°was achieved for PTFE coatings deposited on a substrate with R a = 4500 nm. The superhydrophobicity observed in these coatings is attributed to the presence of dual scale roughness, densely packed microstructure and the presence of CF 3 groups. Unlike the bulk PTFE which is mainly dispersive, the sputter deposited PTFE coatings are expected to have some degree of polar component due to the plasma treatment. In order to calculate the dispersive SFE of PTFE coatings, we have used the Girifalco-Good-Fowkes ͑GGF͒ method and validated it with the Zisman model. Furthermore, the Owens-Wendt model has been used to calculate the dispersive and the polar components of the apparent SFE of the PTFE coatings. These results are further corroborated using the Fowkes method. Finally, an "equation of state" theory proposed by Neumann has been used to calculate the apparent SFE values of the PTFE coatings.
Development of Superhydrophobic Surfaces via Isotropic Etching and Plasma Sputter Deposition
Ceramics in Modern Technologies, 2019
The partial masking followed by the chemical etching is a well-developed method in the fabrication of microelectromechanical systems (MEMS). When there is an anisotropic chemical etching demand, the aqueous solution tends to have extremely oxidizing compounds especially hydrogen fluoride (HF). Consequently, the traditional masking methods such as photolithography which is based on the photoresist polymers may fail to protect the substrate as polymers also become removed by such a harsh etching solution. In the current study, a two-step deposition and chemical etching method is developed to form micron-sized arrays of silicon micropillars. A set of <100> silicon wafers undergoes a physical vapor deposition (PVD) of a silicon carbide (SiC) thin film. Prior to the deposition, an extremely fine mesh made of woven thin stainless steel wires is used to partially cover Si substrates. As a result, an array of micron-sized patches of SiC is deposited underneath each opening of the mesh while the rest of the substrate remains uncoated. In the next phase, the substrate is immersed in a highly corrosive solution (a mixture of hydrofluoric acid, nitric acid, and acetic acid). After giving some minutes of chemical etching, the uncoated parts of the substrate suffer from the etching process while those micron-sized patches formed previously to protect the substrate against the severe corrosive solution. Consequently, the bare silicon exposed to the solution is corroded and leaves a micron-sized pillar beneath the protective SiC coat. The etched substrates are used latterly to receive a thin film of the hydrophobic material such as polytetrafluorethylene (PTFE). The AFM analysis shows the topography of the surface and the morphology of the etched surface is studied by using the scanning electron microscopy (SEM). The results demonstrate extremely high wetting contact angle of the mentioned surface. It is proved that there is an optimum corrosion time which leads to the highest contact angle.
Journal of Micromechanics and Microengineering, 2011
Hydrophobic surfaces with microscale roughness can be rendered ultrahydrophobic by the addition of sub-micron-scale roughness. A simple yet highly effective concept of fabricating hierarchical structured surfaces using a single-step deep reactive ion etch process is proposed. Using this method the complexities generally associated with the fabrication of two-tier roughness structures are eliminated. Three two-tier roughness surfaces with different roughness parameters are fabricated and tested. The surfaces are characterized in terms of the static contact angle and roll-off angle, and are compared with surfaces consisting of only single-tier microscale roughness. The evaporation characteristics of a sessile droplet on the hierarchical surfaces is also assessed relative to comparable single-roughness (SR) surfaces. The robustness of the new hierarchical roughness surfaces is verified through droplet impingement tests. The hierarchical surfaces exhibit very high contact angle and lower contact angle hysteresis compared to the SR surfaces and are more resistant to wetting. The energy loss during impact on the surfaces is quantified in terms of the coefficient of restitution for droplets bouncing off the surface.
Applied Surface Science, 2014
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.
Stable polytetrafluoroethylene superhydrophobic surface with lotus-leaf structure
Journal of Colloid and Interface Science, 2009
A stable polytetrafluoroethylene superhydrophobic surface is prepared with filter paper which is first used as a template. Scanning electron microscope image shows a lotus-leaf like structure appears on the polytetrafluoroethylene surface. Altering the sintering temperature, the microstructure of the as-prepared surface also varied. After treating 12 h in acid, alkali or organic solvents, the as-prepared surface still retains superhydrophobicity and shows excellent stability.
Durable superhydrophobic PTFE films through the introduction of micro- and nanostructured pores
Applied Surface Science, 2015
A superhydrophobic surface, highly water repellant and self-cleaning, is typically made by introducing micro-and nanoscale roughness onto the surface of a low surface energy material. Herein, we offer a new process of superhydrophobic film formation, accomplishing the same thing through the production of micro-and nanoscale surface porosities. Such a material is prepared by introducing zinc acetate (ZnAc 2) and sodium chloride (NaCl) into a commercially available PTFE (polytetrafluoroethylene) emulsion. On drying, baking and washing with acetic acid, the PTFE film produced from the emulsion had both microand nanoscale surface porosities, and demonstrated superhydrophobic properties, with a static contact angle >150 • and a slide angle <10 •. From SEM observation, NaCl contributes microscale porosity, while ZnAc 2 decomposes to ZnO, contributing nanoscale porosity. Using either ZnAc 2 or NaCl alone produces a surface with a static contact angle >150 • , but with a slide angle >10 •. Based on XPS and SEM data, we explore herein the affect of chemistry and porosity on the mechanism of superhydrophobic surface formation, and the durability of that surface under abrasion.