In the world of single atoms and molecules, Turing structures can spontaneously form - the same ones that are responsible for the irregular, but periodic shapes of zebra stripes. This was demonstrated for the first time by Polish-Danish team of physicists.
The unusual shapes of the stripes on zebra bodies do not come out of nowhere. They are preserved chemical reaction fronts. These reactions take place in accordance with the process described for the first time by the famous British mathematician Alan Turing (protagonist in the recent movie "Imitation Game"). In the world of chemistry, Turing structures often manifest in the form of periodic changes in the concentrations of chemicals. So far, they have been observed only in the structures with sizes of microns and larger. It seemed that at smaller scales - in the nano-world, where the movements of individual atoms and molecules are governed by random fluctuations - these structures do not have the right to form spontaneously, as reported in the Institute of Physical Chemistry PAS release sent to PAP. The results were published last year in The Journal of Chemical Physics.
"Until now, no one has examined the possibility of the formation of Turing structures involving individual atoms or molecules. However, our results show that Turing nanostructures may exist. And they are possible, they can find very specific applications in nanotechnology and materials science" - said Dr. Bogdan Nowakowski from the Institute of Physical Chemistry PAS in Warsaw, one of the physicists in the Polish-Danish team, which recently conducted computer simulations and theoretical analyses concerning Turing nanostructures.
Turing structures exist in dynamical systems far from equilibrium. Under appropriate conditions, coupling may occur: the chemical reactions affect the concentrations of their components, which in turn changes the course of the reaction. The process leads to the formation of periodic, but not necessarily monotonously regular structures. In nature, these structures play an important role, especially in the formation of young organisms (morphogenesis). For example, in the initial phases of the development of vertebrate embryos, in the dorsal mesoderm form periodic segments, somites, which are later converted into vertebrae, elements of the spine.
"In our study we considered very simple reactions of two model substances with different rate of diffusion. Computer simulations carried out using molecular dynamics, in collaboration with Dr. Jesper Hansen from the Danish University of Roskilde, provided a very interesting image" - said Dr. Piotr Dziekan from the Institute of Physical Chemistry PAS.
In the simulated nanometer systems, clear and permanent structures spontaneously formed: periodic changes in the density of molecules, which remained stable despite the destructive influence of fluctuations. It turned out that one cycle of concentration changes within the Turing structure may appear already on a length of 20 molecules.
For Turing nanostructures to form, chemical reactions between chemicals must meet certain conditions. This requirement significantly reduces the number of compounds that can participate in the process and, consequently, limits the potential applications. However, the simulations carried out by the Polish-Danish team suggest that Turing nanostructures can quite easily be transferred onto other compounds that do not directly participate in the main reaction.
"Turing nanostructures can be formed only with the participation of carefully selected chemicals. Fortunately, the generated structure can be >>pressed<< onto the concentrations of other chemicals. To copy the structure, these compounds must fulfil only two simple conditions: they must bind to one of the main reactants and diffuse slowly" - explained Dr. Dziekan.
The possibility of the formation of Turing structures in sections of the order of nanometers opens the door to interesting applications, particularly in the field of surface modification of materials. By skilfully selecting the chemical composition of the reagents and the conditions in which the reaction occurs, it may be possible to form Turing structures developing in two dimensions (on the surface of the material), or three dimensions (also in the space adjacent to the surface). The structures may then be preserved, for example by photopolymerization, thereby obtaining a stable, extended surface with a complex, periodic structure.
Research on Turing nanostructures have been funded in the International PhD Projects programme of the Foundation for Polish Science.
PAP - Science and Scholarship in Poland
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