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Company News About A typical Belousov-Zhabotinsky pattern of concentric circles, observed in this case in polymer-controlled crystallisation and self-organisation from barium carbonate.

A typical Belousov-Zhabotinsky pattern of concentric circles, observed in this case in polymer-controlled crystallisation and self-organisation from barium carbonate.

2017-12-15
A typical Belousov-Zhabotinsky pattern of concentric circles, observed in this case in polymer-controlled crystallisation and self-organisation from barium carbonate.
 
   A typical Belousov-Zhabotinsky pattern of concentric circles, observed in this case in
 
polymer-controlled crystallisation and self-organisation 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.
 
 
 

   In order to survive, biological systems need to form patterns and organise

 

themselves. Scientists at the Max Planck Institute for Colloids and Interfaces in

 

Potsdam, Germany, have now combined self-organisation with chemical pattern

 

formation.They coupled an oscillating chemical reaction with polymer-controlled

 

crystallisation and self-organisation in barium carbonate. In this way, they proved that

 

oscillating reactions - like the renowned Belousov-Zhabotinsky reaction - can also take

 

place in multi-phase systems.

 

  On basis of these results, scientists can better explain chemical reactions which are

 

out of thermodynamic balance, as well as biological pattern formation in nature.

 

Furthermore, these results could lead to the creation of surfaces with new kinds of

 

structures (Angewandte Chemie, June 21, 2006).

 

Scientists are especially interested in oscillating chemical reactions. These occur when

 

reaction products periodically and repeatedly change. Their behaviour 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

 

coloured 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 it is not just chemical reactions which 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.

 

   Researchers from Potsdam have now proven that these oscillating reactions can

 

also apply to multi-phase systems, and even to the self-organisation 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.

   

  The researchers used a newly synthesized polymer to create the typical concentric

 

circle pattern, via controlled barium carbonate crystallisation (see image). Such

 

patterns correspond quite well to the calculations in a simulation. The researchers also

 

were able to formulate a complex coupled reaction system including crystallisation,

 

complexation, and precipitation reactions and identify the autocatalytic formation of a

 

complex between barium and the polymer.

 

    Notably, the elongated crystalline structures which made up the circular pattern are

 

themselves created by superstructures of nanoparticles, which are themselves created

 

by self-organisation (see image). 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-organisation. 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-organisation is mussel shell patterns. They are created via controlled

 

crystallisation, just like the model systems of the researchers in Potsdam used.    

 

  Interestingly, these patterns also mathematically duplicate reaction-diffusion systems

 

exactly.