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Discovered in the 1950s, the Belousov-Zhabotinsky reaction
is a self-oscillating redox reaction that was originally
found to occur in solution.
The oscillatory waves are readily visualized,
due to the changing color, or oxidation state of a metal
In an unstirred solution, where no chemicals
are being added or removed from the system,
target or spiral waves develop and propagate
throughout the solution.
By incorporating the metal catalyst for the reaction
into a polymer hydrogel, we are able to confine the reaction
to a millimeter sized gel, to show
that pattern formation within the material,
can be controlled by changing the gel shape and size.
These self-sustained oscillations evolve over time,
and last for several hours.
Here, the period of oscillation is approximately two minutes.
When the reaction is further restricted to a gel of size,
less than a millimeter, the material
exhibits chemical oscillations that
are coupled to the mechanical swelling and shrinking
of the gel.
These self-sustained pulsations exhibited by the BZ gel,
enable unique applications using this material as a sensor
or actuator capable of responding
to small changes in its chemical environment.