Chemistry Reference
In-Depth Information
Chapter 5
Oscillating Droplets: Chemical
Micro-Oscillators
Emulsion droplets running the Belousov-Zhabotinsky reaction
form chemical micro-oscillators and their coupling /
synchronization behaviour via bilayer membranes is discussed.
5.1 Introduction
The synchronization of coupled oscillators is a striking manifestation of self-
organization that nature employs to orchestrate essential processes of life, such as
the beating of the heart. Chemical reaction-diffusion processes have been paradig-
matic systems in understanding such synchronization. The most thoroughly studied
oscillating chemical reaction is the so-called Belousov-Zhabotinski (BZ) reaction
[
1
-
3
]. There are several formulations which have been used. Most of them contain
an autocatalytic step decomposing bromate (BrO
3
) as the main educt, with the help
of an oxidizer, such as Fe
III
ions. The reduction of the Fe
II
to Fe
III
provides an
optical indicator for this step, which can be enhanced by using the ferroin complex
as a carrier for the Fe ions. The progress of the reaction is then accompanied by a
color change from deep red to light blue. The product, BrO
2
, acts as a catalyst, or
'promotor' in this first step. A second step involving malonic acid is coupled to this
system, which by re-oxidizing the Fe
III
to Fe
II
produces bromine ions. The latter
react with the BrO
2
promotor to yield BrO
−
as the final product. The bromine thus
scavenges the promotor of the autocatalytic step, and is therefore considered as the
'inhibitor'.
After having been almost unrecognised after its discovery for many years, the BZ
reaction has later become one of the paradigm systems for dynamical systems and
