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