Comparative study of the impact and sliding behavior of water droplets on two different hydrophobic silane coatings

Nakajima, Akira; Miyamoto, Takumi; Sakai, Munetoshi; Isobe, Toshihiro; Matsushita, Sachiko

doi:10.1016/j.apsusc.2013.12.097

Cited by 20 publications

(7 citation statements)

References 36 publications

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“…Therefore, we may consider that these interactions cause kinetic energy dissipation in the drop. Nakajima et al 43 calculated that this dissipation depends on the contact area between the drop and the surface. At We < 150, drop spreading is limited, thus the water−surface contact area is small and the interaction is negligible.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?

et al. 2016

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ABSTRACT:It is well known that a superhydrophobic surface may not be able to repel impacting droplets due to the socalled Cassie-to-Wenzel transition. It has been proven that a critical value of the receding contact angle (θR) exists for the complete rebound of water, recently experimentally measured to be 100° for a large range of impact velocities. On the contrary, in the present work, no rebound was observed when low surface tension liquids such as hexadecane (σ = 27.5 mN/m at 25°C) are concerned, even for very low impact velocities and very high values of θR and low contact angle hysteresis. Therefore, the critical threshold of θR ≈ 100° does not sound acceptable for all liquids and for all the hydrophobic surfaces. For the same Weber numbers a Cassie-to-Wenzel state transition occurs after the impact due to the easier penetration of low surface tension fluids in the surface structure. Hence a criterion for drop rebound of low surface tension liquids must consider not only the contact angle values with surfaces, but also their surface tension and viscosity. This suggests that, even if it is possible to produce surfaces with an enhanced static repellence against oils and organics, generally the realization of synthetic materials with remaining self-cleaning and anti-sticking abilities in dynamic phenomena, such as spray impact for example, still remains an unsolved task. Moreover, it is demonstrated that also the chemistry of the surface and the physico-chemical interactions with the liquid drops and the possible wettability gradient of the surface asperity play an important role in determining the critical Weber number above which impalement occurs. Therefore the classical numerical simulations of drop impacts onto dry surfaces are definitively not able to capture the final outcomes of the impact for all the possible fluids, if the surface topology and chemistry and/or the wettability gradient in the surface structure are not properly reflected.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?

et al. 2016

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“…The relatively smaller CA value for the surface coated with 6-AHAS can be explained by the presence of more amine groups that increases the likelihood of forming hydrogen bonds with the surrounding water molecules. 23 Quaternization of the surface coated with 3-APS further increased the hydrophilicity with an angle of ∼50°. This occurs because one of the H atoms in the amine group is replaced by alkyl groups (C 2 H 5 ) from the ethyl iodide precursor and the subsequent formation of quaternary ions (R 4 N + ) that are hydrophilic in nature due to the polar bonding.…”

Section: Resultsmentioning

confidence: 99%

“…This significant reduction is attributed to the intrinsic hydrophilicity of the amine groups present in the silanes. The relatively smaller CA value for the surface coated with 6-AHAS can be explained by the presence of more amine groups that increases the likelihood of forming hydrogen bonds with the surrounding water molecules …”

Section: Results and Discussionmentioning

confidence: 99%

Enhanced Filtration Characteristics and Reduced Bacterial Attachment for Reverse Osmosis Membranes Modified by a Facile Method

et al. 2021

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In this study, we report the facile surface modification of reverse osmosis (RO) membranes for improved filtration as well as bacterial resistance properties. Thin films of two silanes, 3-aminopropyltriethoxysilane (3-APS) and 6-aminohexylaminotriethoxysilane (6-AHAS), were dip-coated on commercial RO membranes, and their nitrogen atoms subsequently quaternized. Analyses of the modified membranes via scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy confirmed the “peak and valley” morphology of the original membrane, silane deposition, and N quaternization, respectively. The original membrane showed a water contact angle of ∼90–100° that was significantly decreased after silane coating: 63° for 3-APS and ∼52° for 6-AHAS. Filtration experiments with a high-salinity feed revealed significant improvements in the permeate flux (∼25–40%) and salt rejection (∼10–15%) after the surface modification. Bacterial adhesion studies with two different species, Bacillus subtilis and Pseudomonas aeruginosa, showed significantly reduced cell attachment on the modified membranes. In addition, the coated and quaternized membranes significantly restricted the biological activity and colony formation of both strains with a bacteriostasis rate of ∼75%. The enhanced filtration and antifouling capabilities of the modified membranes were attributed to the presence of polar functionalities (R4N+).

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“…The bilayer of the TESPA-OTS polymeric nanofilm can easily achieve the superhydrophobic property by a two-step immersion procedure without the assistance of high temperature, long reaction time and advanced apparatus, compared with bilayers developed by applying other long-chain alkoxy silanes (e.g., surfaces modified with ODTES usually take more than 12 hours above 80 °C). [31][32][33] As confirmed by XPS, CA and electrochemical measurements, 25,26 the TESPA polymeric nanofilm possesses plenty of silanol groups that offer an opportunity for the etched copper mesh to be superhydrophilic. In order to explore the potential hydrophilicity of the TESPA polymeric nanofilm, permeating behaviors of 10 μL water on the studied mesh surfaces were analysed and compared with Fig.…”

Section: Determination Of Contact Angle and Permeating Behavioursmentioning

confidence: 97%

A multifunctional polymeric nanofilm with robust chemical performances for special wettability

et al. 2016

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A multifunctional polymeric nanofilm of a triazinedithiolsilane compound, which can protect metallic substrates and activate the corresponding surface simultaneously, is introduced onto a copper mesh surface via facile solution-immersion approaches. The resultant interface exhibits hydrophilic features due to the existence of silanol groups (SiOH) outward and has the potential to act as a superhydrophilic and underwater superoleophobic material. As the polymeric nanofilm atop the copper mesh is modified with long-chain octadecyltrichlorosilane (OTS), the functionalized surface becomes superhydrophobic and superoleophilic. The OTS-modified polymeric nanofilm shows outstanding chemical durability and stability that are seldom concurrently satisfied for a material with special wettability, owing to its inherent architecture. These textures generate high separation efficiency, durable separation capability and excellent thermal stability. The protective ability, originating from the textures of the underlying cross-linked disulfide units (-SS-) and siloxane networks (SiOSi) on the top of the nanofilm, prolongs the chemical durability. The activating capability stemming from the residual SiOH groups improves the chemical stability as a result of the chemical bonds developed by these sites. The significant point of this investigation lies in enlightening us on the fabrication of multifunctional polymeric nanofilms on different metal surfaces using various triazinedithiolsilane compounds, and on the construction of interfaces with controllable wettable performances in demanding research or industrial applications.

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Comparative study of the impact and sliding behavior of water droplets on two different hydrophobic silane coatings

Cited by 20 publications

References 36 publications

Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?

Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?

Enhanced Filtration Characteristics and Reduced Bacterial Attachment for Reverse Osmosis Membranes Modified by a Facile Method

A multifunctional polymeric nanofilm with robust chemical performances for special wettability

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