Initially separated reaction-diffusion systems

Characteristics of the A + B → C reaction-diffusion system with initially separated components are studied theoretically and experimentally. When the reaction is slow, the two species will mix before reacting. This leads to a series of crossovers from a rich initial behavior to an asymptotic time behavior. The crossovers depend on the system parameters, such as the diffusion coefficients and initial densities of the two species. In this paper we review our recent studies on this system. We elaborate on a theoretical study of momentum effects, and then focus on theoretical explanations of two experimental phenomena: 1) Non-universal and non-monotonic motion of the reaction front center. The latter occurs when one of the reactants has larger diffusion coefficient but smaller initial density. 2) Existence of more than one front. This occurs when two different transformations of the same reactant (on one of the sides of the system), react with the reactant on the other side with a different reaction constant - the majority slowly, but the minority much faster.