Nanoparticle ‘schools’ reveal new state of matter

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A new state of matter, generated by collective behaviors of particles similar to those presented by some living species, was discovered by Nikolai Brilliantov, a mathematician at the Skolkovo Institute of Science and Technology in Russia, expanding an area of ​​science that rarely gains unprecedented contours.

According to Newton’s Second Law, “the resulting force acting on a body is proportional to the product of the mass by the acceleration it acquires.” Therefore, an object moves faster or slower when it receives a “push” depending on its characteristics.

However, Brilliantov points out, much of the world’s matter is active and acts under its own conditions. Bacteria, birds, fish and humans, for example, are able to dialogue with what affects them. Incidentally, the same can happen with non-living elements.

In this category are nanoparticles known as “Janus particles”, composed of two sides with different chemical properties, which allows them to undertake movements beyond the reach of those that are passive to the forces of nature.

To understand a little more about the little ones, Brilliantov and his team then decided to apply them to computational models. That’s when they got a surprise.

From the analyzes carried out by the researchers, it was found that, despite not consciously interacting with the environment, active nanoparticles acted as bacteria or specimens with internal sources of energy without information processing skills, resulting in the “shoal state”, in free translation.

“Nobody rules over me”

First, scientists explain, in passive matter, different states can coexist. Even if the water in a glass evaporates and becomes gaseous little by little, they exemplify, the one that remains behind is still liquid. On the other hand, with active matter, this does not happen. It is all liquid, all solid or all gas, with no middle ground.

In addition, they add, these nanoparticles are grouped in large conglomerates – or quasiparticles -, which mix in a circular pattern around a central void, like a swirl of sardines. The idea of ​​naming these configurations “schools” and what form “school status” came from this scenario.

Do you think that the novelty bends to the traditional rules? No way. In the aforementioned state of turbulence, the particles violate Newton’s Second Law, ceasing to accelerate under the application of a force and keeping the course at the same pace they followed before the intervention.

“They just move at a constant speed, which is absolutely surprising,” says Brilliantov.

From theory to practice

Published in Scientific Reports in October 2020, the results achieved relate to basic simulations. For this reason, the mathematician and his team intend to create more complex models, also inserting particles of active matter with information processing capacity, more similar to insects, which can help to deepen what governs agglomerations of the type.

“It is very important that we see that the nature of active matter” is much richer than that of passive matter, argues Nikolai, who does not rule out, in the end, the creation of self-assembling materials.