Scanning Drop Friction Force Microscopy

Hinduja, Chirag; Laroche, Alexandre; Shumaly, Sajjad; Wang, Yujiao; Vollmer, Doris; Butt, Hans‐Jürgen; Berger, Rüdiger

doi:10.1021/acs.langmuir.2c02046

Cited by 17 publications

(26 citation statements)

References 42 publications

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“…The surface could remain superhydrophobic after this process. After 10 freezing/melting cycles, we measured the friction force required to move a 10 µL water drop on the surface using a drop adhesion force instrument 66,67 . The result (Supporting Information: Section ) shows that compared to that on PDMS‐SH surface, the maximum force for a water drop on L‐PDMS‐SH (7.5%) to start moving did not change a lot after the 10 cycles of test.…”

Section: Resultsmentioning

confidence: 99%

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Chemically robust superhydrophobic surfaces with a self‐replenishing nanoscale liquid coating

Zhou,

Sudersan,

Diaz

et al. 2024

Droplet

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Due to poor chemical robustness, superhydrophobic surfaces become susceptible to failure, especially in a highly oxidative environment. To ensure the long‐term efficacy of these surfaces, a more stable and environmentally friendly coating is required to replace the conventional salinization layers. Here, soot‐templated surfaces with re‐entrant nanostructures are precoated with polydimethylsiloxane (PDMS) brushes. An additional nanometer‐thick lubricant layer of PDMS was then applied to increase chemical stability. The surface is superhydrophobic with a nanoscale liquid coating. Since the lubricant layer is thin, ridge formation is suppressed, which leads to low drop sliding friction and fast drop shedding. By introducing a bottom “reservoir” of a free lubricant as an oil source for self‐replenishing to the upper layer, the superhydrophobic surface becomes more stable and heals spontaneously in response to alkali erosion and O2 plasma exposure. This design also leads to a higher icing delay time and faster removal of impacting cooled water drops than for uncoated surfaces, preventing icing at low temperatures.

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Section: Resultsmentioning

confidence: 99%

“…After 10 freezing/melting cycles, we measured the friction force required to move a 10 µL water drop on the surface using a drop adhesion force instrument. 66,67 The result (Supporting Information: Section 6)…”

Section: Resultsmentioning

confidence: 99%

Chemically robust superhydrophobic surfaces with a self‐replenishing nanoscale liquid coating

Zhou,

Sudersan,

Diaz

et al. 2024

Droplet

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“…Chemically heterogeneous samples have been prepared by the process of double chemical vapor deposition with the use of a glass mask. 37 Standard microscopic glass slides were cleaned with Milli-Q water, then with acetone, ethanol, and 5 min oxygen plasma treatment at 300 W and 0.3 bar (Diener Electronic Femto). Then, they were treated by chemical vapor deposition of PFOTS in a desiccator.…”

Section: Methodsmentioning

confidence: 99%

Deep Learning to Analyze Sliding Drops

Shumaly

Darvish

et al. 2023

Langmuir

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State-of-the-art contact angle measurements usually involve image analysis of sessile drops. The drops are symmetric and images can be taken at high resolution. The analysis of videos of drops sliding down a tilted plate is hampered due to the low resolution of the cutout area where the drop is visible. The challenge is to analyze all video images automatically, while the drops are not symmetric anymore and contact angles change while sliding down the tilted plate. To increase the accuracy of contact angles, we present a 4-segment super-resolution optimized-fitting (4S-SROF) method. We developed a deep learning-based super-resolution model with an upscale ratio of 3; i.e., the trained model is able to enlarge drop images 9 times accurately (PSNR = 36.39). In addition, a systematic experiment using synthetic images was conducted to determine the best parameters for polynomial fitting of contact angles. Our method improved the accuracy by 21% for contact angles lower than 90°and by 33% for contact angles higher than 90°.

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“…In this work, we show that the substrate and the coating can change slide electrification in a more complex way. The glass was coated by chemical vapor deposition (CVD) with perfluorooctyltrichlorosilane (PFOTS) ,,, or octyltrichlorosilane (OTS) , to generate a hydrophobic layer. To analyze the influence of both the substrate chemistry and the coating, we measured droplet charging for different substrates and different coatings.…”

Section: Introductionmentioning

confidence: 99%

How Surface and Substrate Chemistry Affect Slide Electrification

Leibauer,

Pop-Georgievski,

Sosa

et al. 2024

J. Am. Chem. Soc.

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When water droplets move over a hydrophobic surface, they and the surface become oppositely charged by what is known as slide electrification. This effect can be used to generate electricity, but the physical and especially the chemical processes that cause droplet charging are still poorly understood. The most likely process is that at the base of the droplet, an electric double layer forms, and the interfacial charge remains on the surface behind the three-phase contact line. Here, we investigate the influence of the chemistry of surface (coating) and bulk (substrate) on the slide electrification. We measured the charge of a series of droplets sliding over hydrophobically coated (1−5 nm thickness) glass substrates. Within a series, the charge of the droplet decreases with the increasing droplet number and reaches a constant value after about 50 droplets (saturated state). We show that the charge of the first droplet depends on both coating and substrate chemistry. For a fully fluorinated or fully hydrogenated monolayer on glass, the influence of the substrate on the charge of the first droplet is negligible. In the saturated state, the chemistry of the substrate dominates. Charge separation can be considered as an acid base reaction between the ions of water and the surface. By exploiting the acidity (Pearson hardness) of elements such as aluminum, magnesium, or sodium, a positive saturated charge can be obtained by the counter charge remaining on the surface. With this knowledge, the droplet charge can be manipulated by the chemistry of the substrate.

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Scanning Drop Friction Force Microscopy

Cited by 17 publications

References 42 publications

Chemically robust superhydrophobic surfaces with a self‐replenishing nanoscale liquid coating

Chemically robust superhydrophobic surfaces with a self‐replenishing nanoscale liquid coating

Deep Learning to Analyze Sliding Drops

How Surface and Substrate Chemistry Affect Slide Electrification

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