Sustained spiral waves in a continuously fed unstirred chemical reactor

Previous experiments on the self-organization of spatial patterns in chemical reactors have generally been restricted to closed (batch) reactors. In such reactors the system relaxes irreversibly and uncontrollably towards thermodynamic equilibrium. It is difficult to make comparisons with existing theories which address asymptotic (long time) behavior because of the transient nature of the spatial patterns and the lack of well-defined control parameters in such experiments. We report a novel disk-shaped reactor that can be maintained far from thermodynamic equilibrium indefinitely by a continuous feed of reagents. Chemical patterns are formed inside a thin layer of inert gel that suppresses any convective motion. The feed to the gel is uniform and normal to the plane in which pattern can form. The reactor is used to conduct the first quantitative study of transitions between well-defined states with different patterns.