Bubble-treated ink droplets help control printed nanoparticle patterns
Tokyo Metropolitan University researchers say ultrafine bubbles can steer how inkjet-deposited nanoparticles dry without leaving chemical residues.
By Tom Brennan · Health & Medicine Correspondent
3 min read
Researchers at Tokyo Metropolitan University say they have found a cleaner way to control the microscopic patterns left by inkjet printing. The method uses ultrafine bubbles in liquid droplets to change how nanoparticles settle as the ink dries, a problem that matters for printed electronics and small mechanical devices.
The work, led by Professor Arata Kaneko and published in Precision Engineering, targets a common limitation in precision inkjet manufacturing. Inkjet systems can place tiny amounts of material on a surface, but the particles suspended in each droplet can move during drying and form uneven deposits.
One familiar version of that problem is the coffee-ring effect. Tokyo Metropolitan University said particles in a drying droplet often collect at the outer rim, leaving a ring-like stain rather than an even film.
Manufacturers can use additives such as surfactants to change surface tension and improve the final coating, according to the university. Those chemicals can remain after the liquid evaporates, however, and may alter the properties of printed materials.
How the bubble method worked
Kaneko’s team avoided chemical modification by adding nanoscale ultrafine bubbles to a water-based suspension of silica nanoparticles. The researchers passed the mixture through an ultrafine-bubble generator, then used an inkjet nozzle to place 1-nanoliter droplets on a silicon substrate.
Tokyo Metropolitan University said changing the number of bubbles in the droplets changed the shape of the dried particle deposit. Droplets with no bubbles showed a clear coffee-ring pattern. Droplets with a moderate amount of bubbles dried into a more uniform coating, while droplets with higher bubble concentrations pushed more particles toward the center.
The university said the bubbles did not change the silica nanoparticles themselves, including their electrical charge. Instead, the bubbles affected the liquid’s surface tension and spreading behavior after the droplet hit the substrate.
A key advantage, according to the researchers, is that the bubbles disappear as the droplet dries. That means the process can influence the drying pattern without leaving behind the kind of residue associated with conventional additives.
Potential use in printed devices
Tokyo Metropolitan University said the approach could be useful for manufacturing next-generation microdevices, including microelectronics and MEMS, or microelectromechanical systems. Those applications often require coatings and circuit patterns to be deposited with high precision at small scales.
The university pointed to gas sensors as one example where deposit shape can matter. It said nanoparticles such as graphene and molybdenum dioxide are used in gas sensors because their electrical conductivity changes when they absorb gases, and sensor sensitivity depends strongly on the printed structure.
The same residue-free feature may also help with conductive nanoparticles used in electronic circuits, according to the university. In those cases, keeping particle surfaces clean can be important for device performance.
The study was authored by Kazuki Shimizu, Takuma Isoya, Takahiro Kono and Arata Kaneko. Tokyo Metropolitan University said the research was supported by JSPS KAKENHI grants JP22H01377 and JP25K01136, and by a JKA Promotion Fund grant, 2024M-394.
This story draws on original reporting from ScienceDaily.