14 DAY TRIAL // In order to survive, biological systems need to form patterns and organize themselves. Scientists at the Max Planck Institute for Colloids and Interfaces in Potsdam, Germany, have now combined self-organization with chemical pattern formation.
Scientists are especially interested in oscillating chemical reactions. These occur when reaction products periodically and repeatedly change. Their behavior is of importance to many fields of study - including chaos research. That is because these reaction systems are always complex and far away from thermodynamic equilibrium. One particularly well-known example is the "Belousov-Zhabotinsky" reaction. In it, a colored indicator is used to make the reaction products of a coupled redox reaction visible. They typically take on the pattern of concentric circles, spreading out, for example, across a petri dish.
Mathematically, spatially oscillating reactions can be described as "reaction-diffusion systems". This means that not only chemical reactions influence the amount of material at a certain point in space. Diffusion also plays a role - the exchange of material with the surrounding area. In such simulations, we get the typical concentric circle pattern of a Belousov-Zhabotinsky reaction. In the picture above, it is indicated in red-violet.
The Belousov-Zhabotinsky pattern of concentric circles was observed in this case in polymer-controlled crystallization and self-organization from barium carbonate. The structures are similar to a computer-simulated pattern (smaller circle, upper right). The block copolymer used appears in the picture as a shortened molecule structure.
The researchers were also able to formulate a complex coupled reaction system including crystallization, complication, and precipitation reactions and identify the autocatalytic formation of a complex between barium and the polymer. In this way, they proved that oscillating reactions - like the renowned Belousov-Zhabotinsky reaction - can also take place in multi-phase systems and can even involve the self-organization processes of nanoparticles.
What is central is that in a multi-phase reaction system, it is possible to formulate either an autocatalyic or autoinhibiting reaction step. This leads an oscillating system to be constructed, and ultimately a pattern to be formed.
Notably, the elongated crystalline structures which made up the circular pattern are themselves created by superstructures of nanoparticles, which are themselves created by self-organization.
In this way, Max Planck researchers have shown for the first time that the Belousov-Zhabotinsky reaction does not just take place in a solution, but also in multi-phase systems, and in nanoparticle self-organization. This discovery is not only important to research into reactions far away from thermodynamic equilibrium. It can also help explain biological pattern formation. One example of biological self-organization is mussel shell patterns. They are created via controlled crystallization, just like the model systems of the researchers in Potsdam used. Interestingly, these patterns also mathematically duplicate reaction-diffusion systems exactly. Furthermore, these results could lead to the creation of surfaces with new kinds of structures.
Image: Max Planck Institute of Colloids and Interfaces