Internal and External Flow over Laser-Textured Superhydrophobic Polytetrafluoroethylene (PTFE)

Ahmmed, K. M. Tanvir; Patience, Christian A.; Kietzig, Anne‐Marie

doi:10.1021/acsami.6b11239

Cited by 51 publications

(54 citation statements)

References 43 publications

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“…The SH riblet sample showed similar wetting behaviour as the SH surface. Trapped air pockets under the water droplet sitting on the SH surface were verified by using a confocal microscope in our earlier study . Moreover, both the SH and SH shark surfaces sustained the air‐trapping wetting state (also called the Cassie state) during flow experiments as verified by visual inspection and shown in Figure S3 in the supplementary information.…”

Section: Resultssupporting

confidence: 88%

“…The roughness of the laser‐ablated SH surface is about an order of magnitude higher than that of a flat non‐ablated surface. The arithmetic average roughness, R a was measured as 0.025 and 0.262 μm for a flat PTFE and the SH sample, respectively . The roughness measurements presented here are an approximation and obtained by 3D confocal microscopy.…”

Section: Resultssupporting

confidence: 56%

“…The SH surface (Figure c) reduced drag in its non‐pre‐wetted condition. The amount of drag reduction is small because the slip length on this PTFE SH sample is small (∼13 μm) as observed earlier in a laminar flow experiment . However, when the sample is pre‐wetted, the drag reduction disappeared, instead, increase in the pressure drop is observed compared to a flat PTFE sample and the non‐pre‐wetted SH sample.…”

Section: Resultsmentioning

confidence: 81%

“…Kietzig, “Internal and external flow over laser‐textured superhydrophobic PTFE,” ACS Applied Materials & Interfaces , 2016 , 8 , 27411–27419. Copyright (2016) American Chemical Society).…”

Section: Methodsmentioning

confidence: 77%

“…Figure 4 shows a SH sample surface which does not have any ridge structure. Figures 4b and 4c show that the SH surface is covered [29] ).…”

Section: Pressure Drop Measurementmentioning

confidence: 93%

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Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

2017

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Salvinia leaf and sharkskin are prime examples of nature's marvel. Salvinia leaf‐inspired superhydrophobic surfaces keep themselves clean and reduce drag in fluid flow. Sharkskin also reduces drag in turbulent flow and inhibits biofouling. Therefore, the prospect of having a drag‐reducing surface with both salvinia leaf and sharkskin properties is attractive. However, fabricating such a surface is difficult, and the current fabrication methods require at least two separate steps. In addition, the mechanisms of drag reduction of salvinia leaf and sharkskin are different, and their combined effect on the flow field is not well understood. In this study, we produced a PTFE surface that mimics sharkskin in its surface pattern and copies the superhydrophobic nature of the salvinia leaf in its microstructure. This surface was fabricated by laser machining and tested in a closed channel under turbulent flow conditions. We measured the pressure drop at different Reynolds numbers on this surface both in pre‐wet and non‐pre‐wet conditions and compared the result with pressure drop data on four other PTFE samples: two types of non‐superhydrophobic sharkskin inspired surface (riblets), a superhydrophobic surface, and a non‐machined surface. Both the non‐superhydrophobic riblets and the superhydrophobic sample reduced drag compared to the non‐machined surface. However, we observed a lack of drag reduction by the superhydrophobic riblets sample. We presented a qualitative explanation for the lack of drag reduction and concluded that the modifications of the flow field by the two drag reduction mechanisms are not beneficial for overall drag reduction in our experiment.

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 56%

Section: Resultsmentioning

confidence: 81%

Section: Methodsmentioning

confidence: 77%

“…Figure 4 shows a SH sample surface which does not have any ridge structure. Figures 4b and 4c show that the SH surface is covered [29] ).…”

Section: Pressure Drop Measurementmentioning

confidence: 93%

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Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

2017

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Robust and Chemically Stable Superhydrophobic Composite Ceramic Coating Repellent Even to Hot Water

Liu

Wang

Zhang

et al. 2017

Adv Materials Inter

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electrospinning, [15] chemical vapor deposition, [16] chemical etching, [17] and electrochemical deposition. [18] Nevertheless, the real scale-up applications of superhydrophobicity were rarely reported due to the complex preparation process of hierarchical structures. There is still a serious problem from academic research to industrial production and applications: How to keep the long-term superhydrophobicity under harsh conditions?Recently, ceramic materials were used as a means of creating hydrophobic surfaces due to their intrinsic chemical inertness, high temperature stability, and good mechanical properties. [19][20][21] For example, Cai et al. [22] presented a rare earth oxide ceramic superhydrophobic coating on stainless steel substrates by solution precursor plasma spray. Fang et al. [23] fabricated hydrophobic alumina hollow fibers with an average pore size of 0.7 µm for water desalination by the phase inversion and grafting with fluoroalkylsilane. Compared with polymeric material, ceramic materials with high hardness and mechanical strength have obvious advantage to provide robust hierarchical structure for superhydrophobic surface under harsh conditions, such as the unavoidable abrasion, corrosion, and water-impact. However, the large-scale applications of ceramic coating are dramatically limited by the intrinsic brittleness of ceramic materials. [24] Therefore, developing a method to overcome the significant defects associated with ceramic can be used as an effective way to increase the stability of superhydrophobic ceramic coating under harsh conditions. Carbon nanotubes (CNTs) with high crystallinity, high aspect ratio, nano-order-scale, and web-like entangled structure have received widespread attention as promising toughening materials. [25,26] The critical issue of CNT-reinforced ceramic is the dispersion of CNTs into the matrix. Balani et al. [27] reported a CNT-reinforced Al 2 O 3 ceramic coating on the steel substrate by plasma spray. CNTs are in situ grown on Al 2 O 3 powder particles by the catalytic chemical vapor deposition (CCVD) technique. The plasma-sprayed coating showed an obvious enhancement in hardness and fracture toughness, proving the enhanced effect of CNTs. However, considering the complicated CCVD process, this method is not propitious to the demand of wholesale industrialization. To overcome the brittleness of ceramic, Robust and chemically stable superhydrophobic composite ceramic coating with internal porous structures and superficial network structures has been successfully prepared through incorporating spray and pore-forming technique. The internal micro-/nanoporous structures are regulated by using H 2 O as pore-forming agent and the superficial network structures are designed by the fibrillated polytetrafluoroethylene (PTFE). Carbon nanotubes (CNTs) modified by dopamine are used to overcome the brittleness of ceramic. The prepared superhydrophobic ceramic/CNT/PTFE coating demonstrates a high water contact angle of 161° ± 1.2° and low sliding angle of 4° ± 0.3°. Simul...

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Enhancement of the hydrophobicity and oleophobicity of a polyurethane coating using a fluorine‐free polyfarnesene‐based polyol

Shiraki

2023

J of Applied Polymer Sci

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The development of hydrophobic and oleophobic surfaces on materials has attracted significant attention in various research fields. Fluoropolymers, which possess low surface energy and are both highly hydrophobic and oleophobic in nature, are widely used to enhance the liquid repellency of materials. However, during fluoropolymer manufacture, fluorine‐containing compounds are released into the environment; thus, alternatives to fluoropolymers are required for maintaining environmental safety and realizing a sustainable society. Notably, the development of such alternative materials has been limited. Thus, we herein report the application of a novel polyurethane (PU) coating synthesized from bio‐based raw materials. The prepared hydrogenated polyfarnesene PU (HHPF PU), which possesses an amorphous bottlebrush‐like polyalkyl structure, was found to exhibit higher hydrophobicity and oleophobicity than polytetrafluoroethylene (PTFE), which is a typical low‐surface‐energy material. The water and n‐hexadecane contact angles of the HHPF PU were determined to be 119° and 68°, respectively, whereas those of PTFE were 108° and 46°, respectively. In addition, the density depth profile of the PU thin film was confirmed through x‐ray reflectometry. This study provides a novel approach for enhancing the hydrophobicity and oleophobicity of materials using bottlebrush‐like polyalkyl structure instead of fluorine.

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Internal and External Flow over Laser-Textured Superhydrophobic Polytetrafluoroethylene (PTFE)

Cited by 51 publications

References 43 publications

Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

Robust and Chemically Stable Superhydrophobic Composite Ceramic Coating Repellent Even to Hot Water

Enhancement of the hydrophobicity and oleophobicity of a polyurethane coating using a fluorine‐free polyfarnesene‐based polyol

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