Physicists in Russia recently investigated the behavior of particles in dusty plasma at a temperature below 2 K, an experiment that revealed nanoclusters forming in the plasma and the synthesis of polymer fibers taking place at extremely low temperatures. According to the team, such results can be used to create new materials with desired and controlled properties.
According to Oleg Petrov, director of the Institute for High Temperatures at Russian Academy of Sciences and one of the authors of the article, this experiment represents the first time that scientists have observed dusty plasma in a gas discharge cooled by superfluid helium at a temperature of 1.6 to 2 K. Until now, Petrov says, dusty plasma and even gas discharges have not been studied at temperatures lower than 4.2 K, a liquid helium temperature.
In the course of the experiment, ion sputtering of polymers from a special insert was carried out and self-organization phenomena were observed, specifically the formation of nanoclusters with sizes less than 100 nm and polymer fibers with a length of up to 5 mm and a diameter of about 10 microns. The fibers were obtained at extreme temperatures but did not collapse even when studied later under normal conditions.
“At ultralow temperatures, it becomes possible to precisely control the composition of the sprayed material, since under these conditions any impurities “freeze” and precipitate,” says Petrov. “As a result, when spraying a substance in the gaseous helium, it is possible to obtain super pure materials which might be the way to obtain fibers with new desired properties. For example, new types of polymers that cannot be obtained by ordinary chemical synthesis. Such materials may be radically different from existing ones”.
The phenomena of self-organization are widespread in nature, according to Petrov, and are extremely diverse and observed in various systems of complexity and scale: from physical, studied in the nanoworld and in astronomy, to biological, social and economic processes.
Such phenomena are characteristic of the so-called open (non-equilibrium) systems, including dusty plasma formed by charged particles of micron size and retained in the plasma of a gas electric discharge. The intense scattering of laser radiation by particles allows scientists to study the systems formed by charged particles, tracking their coordinates and speeds in real time. Dusty plasma is a convenient tool for studying various phenomena, such as three-dimensional and two-dimensional phase transitions as well as the formation of non-linear waves.
Compared with alternative systems, dusty plasma provides a unique opportunity to vary the temperature of the plasma forming gas—gaseous helium—which helps to study the effect of gas temperature changes on properties of plasma and the processes that occur in it.
The question of the lower limit of temperatures at which experimental studies of dusty plasma can be carried out remained open until recently, according to Petrov. From this point of view, the experiment conducted by Russian physicists on the synthesis of polymer nanoclusters and fibers at temperatures below 2 K is the first in world practice, while only a few comparative studies of dusty plasma at 4.2 K have been conducted so far.
The experiment, the results of which were published in Scientific Reports, was carried out in a facility using an optical cryostat and intended to study plasma-dust structures at helium temperatures. At present, scientists of the JIHT RAS plan to continue the experiments and study the phenomena of self-organization in dusty plasmas at ultralow temperatures using various dispersed materials.