Tiny ion exchange resin beads may allow you to write in water

However, in a liquid, particles are continually moving about, and ink disperses fast. 

A team of researchers from the Johannes Gutenberg University Mainz in Germany has demonstrated a resin ion exchange bead-based technique to draw lines and patterns in water containing ink particles. 

"We have put the ink directly in the water and use a microbead made of ion-exchange material with a diameter of 20 to 50 microns as a writing instrument," explained Thomas Palberg of JGU in an official release. 

The team asserts that this development is at a nascent stage and performed at an incredibly small scale. 

How does it work on water?

In the water, the small bead has no swirling effect, allowing the drawn patterns to stay in place. 

The bead functions by exchanging leftover cations in the water for protons, which allows it to alter the water's local pH value. When a bead rolls across the surface of a water bath, it leaves an imperceptible trail of reduced pH in the liquid. 

“This attracts the ink particles and they accumulate in the path marked out by the ballpoint. The result is a fine line of just a few hundredth microns in width, marking out the area of the lowest pH value,” explained the release. 

The statement mentions that in order to write a letter in water, simply tilt the water bath such that the bead follows the desired path to outline the required character.

"During our first attempts, we moved the water bath by hand but we have since constructed a programmable rocker. In a water bath no bigger than a one Euro coin, we were able to produce a simple house-like pattern in the size of the title of an 'I' character in an 18-point font and then viewed this under the microscope. But we are still only in the preliminary phase,” Palberg added. 

This approach could be used to write letters with continuous lines as well as those with breaks between different letters. The team mentions that it is even feasible to erase and correct what has been written. 

Pens made of particles could also enable writing in water

Further simulations revealed that this process may be carried out in a variety of ways other than with ion exchange beads. 

"In addition to beads made of ion exchange resins, 'pens' consisting of particles that can be heated by lasers could be employed, or even individually steerable microswimmers. This could even allow extensive parallel writing of structures in water. Hence, the mechanism could also be used to generate highly complex density patterns in fluids," said Benno Liebchen, head of the Theory of Soft Matter group at the Institute for Condensed Matter Physics (IPKM) at TU Darmstadt. 

The preliminary experiment establishes a fundamental foundation, implying that writing in water may be viable. 

The results were reported in the journal Small. 

Study abstract:

Writing is an ancient communication technique dating back at least 30,000 years. While even sophisticated contemporary writing techniques hinge on solid surfaces for engraving or the deposition of ink, writing within a liquid medium requires a fundamentally different approach. The study here demonstrates the writing of lines, letters, and complex patterns in water by assembling lines of colloidal particles. Unlike established techniques for underwater writing on solid substrates, these lines are fully reconfigurable and do not require any fixation onto the substrate. Exploiting gravity, an ion-exchange bead (pen) is rolled across a layer of sedimented colloidal particles (ink). The pen evokes a hydrodynamic flow collecting ink-particles into a durable, high-contrast line along its trajectory. Deliberate substrate-tilting sequences facilitate pen-steering and thus drawing and writing. The experiments are complemented with a minimal model that quantitatively predicts the observed parameter dependence for writing in fluids and highlights the generic character of writing by line-assembly. Overall, the approach opens a versatile route for writing, drawing, and patterning fluids—even at the micro-scale