This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Whether on a windowpane at home or during the industrial cleaning of computer chips: droplets sliding over solid surfaces become electrically charged. Yet the physical mechanism behind this charging remains a subject of debate.
This charging is usually attributed to the exchange of charged particles (ions) at the interface between the droplet and the surface. Researchers at the Max Planck Institute for Polymer Research have now investigated two different types of liquids—so-called polar and nonpolar liquids—in both their liquid and frozen states. The researchers discovered that there is apparently at least one additional effect behind droplet charging.
The findings are published in the journal Nature Physics. When droplets glide across surfaces, they usually become positively charged and leave a negatively charged trail on the surface. This process is known as slide electrification.
The resulting electric charges influence the movement of droplets on various surfaces. On a windowpane, for example, this contributes to droplets occasionally getting stuck. During the cleaning of computer chips in industrial manufacturing processes, this can even damage sensitive components.
Therefore, understanding which fundamental processes contribute to droplet charging is of great interest. Currently, charge transfer is typically explained using the concept of the electrochemical double layer: When a droplet contacts a surface, negatively charged ions usually spontaneously attach themselves to the wetted surface. These, in turn, attract mobile positive countercharges from the liquid, which are located just a few nanometers from the surface within the liquid.
As the droplet slides across the surface, negative charges remain on the surface and the droplet becomes positively charged. To investigate the underlying mechanisms, the researchers compared the behavior of two different types of liquids—polar and nonpolar liquids—in both liquid and frozen states. A common example of a polar liquid is water, which conducts electricity, whereas oil, as a nonpolar liquid, does not conduct electrical current.
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