Reaction-diffusion phenomena in antagonistic bipolar diffusion fields.

Operating natural or artificial chemical systems requires nonequilibrium conditions under which temporal and spatial control of the process is realizable. Open reaction-diffusion systems provide a general way to create such conditions. A key issue is the proper design of reactors in which the nonequilibrium conditions can be maintained. A hydrogel with flow-through channels is a simple, flexible, and easy-to-make device in which chemical reactions are performed in the diffusion field of localized separated sources of reactants. Two reactants separated in two channels create a bipolar antagonistic diffusion field, where the reaction intermediates firmly separate in space. Numerical simulations and corresponding experiments are performed to present this inhomogeneous diffusion field-induced chemical separation in sequential reactions. A remarkable result of this bipolar spatial control is localized wave phenomena in a nonlinear activatory-inhibitory reaction. These findings may help design functioning artificial nonequilibrium systems with the desired spatial separation of chemicals.