SPACE — Scientists have found a way to write directly into liquid water. They create clear, long-lasting patterns that float beneath the surface of the liquid.
In new experiments published in the journal Nano Micro Small on August 21, 2023, Benno Liebchen and colleagues at the Technical University of Darmstadt and Germany’s Johnannes Gutenberg University have developed a method for creating long-lasting writing in liquids.
The writing of water relies on a chemical process called diffusioosmosis, which is the spontaneous movement of different types of particles, caused by differences in concentration in a liquid mixture. The liquid mixture, containing low concentrations of charged particles called ions, acts as paper.
Meanwhile, the ink consists of large colloidal (solid) particles, which are spread thinly throughout the solution. The pen is a small ion exchange bead, a particle capable of exchanging charged particles in a liquid mixture with smaller, differently charged particles.
“When you exchange larger ions for smaller ions, the smaller ions can move (diffuse) faster and this causes a difference in concentration,” Liebchen told Live Science.
“This concentration gradient in ion distribution forces the liquid at the bottom of the container, near where the beads move. The moving fluid carries visible colloidal particles (as ink) with it.”
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By rotating liquid paper, Liebchen and Palberg harnessed gravity to guide an ion exchange bead pen through the solution. This will create a different pattern.
As the bead moves through the liquid paper, the colloid particles are pulled behind it due to the concentration gradient effect. That reaction produces a visible line where the pen was.
“Importantly, because the pen is small, it doesn’t disturb the surrounding solvent as much, a larger pen would stir up the water and destroy what you wrote,” Liebchen said.
Colloidal particles do not move much in still water on the experimental time scale because they are too large and heavy. That’s why the lines remain visible.
The team developed the technique using water as paper and silica particles as ink. Next, they explored whether other combinations of paper, pen, and ink might work.
“Many aspects of the writing approach are quite powerful in terms of changing those components, but of course there are limitations,” Liebchen said.
2023-09-28 11:30:00
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