The influence of ions and humidity on charging of solid hydrophobic surfaces in slide electrification

“…The surface charge and electrokinetic properties of liquids in contact with hydrophobic surfaces have been investigated extensively. − However, the introduction of a gas phase appears to complicate the analysis and the contact charge transfer observed when a three-phase contact line moves over a fluoropolymer surface is not well understood. Several studies have revealed that the charge transfer may increase or decrease with ion concentration, − , and this has recently been explained to be due to a combination of shear, which removes charge in the electrical double layer with quenching of the active sites near the fluoropolymer . However, it is not clear how other aqueous liquids miscible with water influence the quenching when hydration takes place near the interface.…”

Section: Introductionmentioning

confidence: 99%

Charge Transfer Quenching and Maximum of a Liquid–Air Contact Line Moving over a Hydrophobic Surface

Helseth

2024

Langmuir

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Charge transfer when a hydrophobic fluoropolymer surface comes in contact with salt solutions of water, methanol, and glycerol is investigated. It is found that the charge transfer decreases faster with an increasing fraction of glycerol in water than it does with methanol in water. It is also demonstrated that for both mixtures, the charge transfer increases with the amount of added sodium chloride for small concentrations but then reaches a maximum and subsequently decreases. Surprisingly, this maximum charge transfer shifts toward higher salt concentrations with increasing amount of glycerol in water. However, in water−methanol mixtures, one does not observe a similar shift in charge transfer maximum toward higher salt concentrations. These observations are explained using a model, taking into account the decreased shear distance from the hydrophobic surface for which ions are removed from the electrical double layer due to an interplay of forces acting on the ions.

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“…17 Recently, the acid−base model (proton donor−acceptor) was used to describe the charge separation in slide electrification, in which a PTFE surface interacts as a proton acceptor or donor. 11 In this context, the effect of pH 10,11,25 and various dissolved ions 11,15,21,25 on the droplet charge has been investigated. It has been proposed that the surface charge acquired by the sliding droplet and the ζ potential in the PTFE−water interface have the same physical basis.…”

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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The influence of ions and humidity on charging of solid hydrophobic surfaces in slide electrification

Abstract: Water drops sliding down inclined hydrophobic, insulating surfaces spontaneously deposit electric charges.

Cited by 4 publications

References 32 publications

Slide electrification of drops at low velocities

Slide electrification of drops at low velocities

Charge Transfer Quenching and Maximum of a Liquid–Air Contact Line Moving over a Hydrophobic Surface

How Surface and Substrate Chemistry Affect Slide Electrification

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