Crystallization as the driving force

"Worm-like Nanostructures"

"Our structures could be described as worm-like rods with decorations," explains Prof. Felix Schacher. "Embedded in these rods are spherical nanoparticles; in our case, this was silica. However, instead of silica, conductive nanoparticles or semiconductors could also be used -- or even mixtures, which can be selectively distributed in the nanocrystals using our method," he adds. Accordingly, the range of possible applications in science and technology is broad, spanning from information processing to catalysis.

Understanding and Controlling the Formation Process

"The primary focus of this work was to understand the preparation method as such," explains the chemist. To produce nanostructures, he elaborates, there are two different approaches: larger particles are ground down to nanometre size, or the structures are built up from smaller components. "We wanted to understand and control this building-up process," Schacher describes. For this, the team used individual silicon dioxide particles, known as silica, and grafted chain-like polymer molecules as a sort of shell.

Directional Crystal Growth

"One could imagine it like hairs on a sphere," the scientist explains. He adds, "These hairs are made of a material called 'poly-(isopropyl-oxazoline)'. This substance crystallises when heated. And that's the idea of our method: crystals almost never grow in all directions simultaneously but prefer a particular direction. This is known as anisotropy. Thus, we were able to grow our nanostructures deliberately."

During this process, the team discovered an intriguing phenomenon. "For the polymer to crystallise, it requires tiny amounts that are not bound to a particle surface but are freely present in the reaction solution, acting as a sort of glue. We found out that the required amounts are so small that they are barely detectable. But they are needed," he adds.