Space- and Time-Resolved Diffusion-Limited Binary Reaction Kinetics in Capillaries: Experimental Observation of Segregation, Anomalous Exponents, and Depletion Zone

An experimental investigation of one-dimensional, diffusion-limited A + B ~ C chemical reactions is reported. The persistence of reactant segregation and the formation of a depletion zone is observed and expressed in terms of the universal time exponents: c~ (motion of the boundary zone), fl (width of instantaneous product formation zone), 7 (rate of instantaneous local formation of product), c~ (rate of instantaneous global formation of product), etc. There is good agreement with the recently predicted and/or simulated values: ~ = 1/2, f l= 1/6, 7=2 /3 , 6 = 1 / 2 , in contrast to classical predictions (c~=0, r 1/2, ~ = 0 , = -1 /2) . Furthermore, classically the segregation would not be preserved and there would be no formation of a depletion zone and no motion (just dissipation) of the reaction zone. We also discuss the relations to electrode oxidat ion-reduction reactions, i.e., A + C--, C where C is a catalyst, electrode, or "trap."