Fickian and non-Fickian diffusion with bimolecular reactions

Yotam Berkowitz, Yaniv Edery, Harvey Scher, Brian Berkowitz

Research output: Contribution to journalArticlepeer-review

Abstract

Mixing zone dynamics of a reaction product C during diffusion of two species (A and B) are examined, using a two-dimensional particle tracking model (PT) for the reaction A+B→C, allowing for both Fickian and non-Fickian transitions. The form of PT we use is equivalent to a continuous time random walk, which is a widely used model for anomalous transport and diffusion. It is shown that the basic patterns of the C dynamics - the temporal evolution of the spatial profile and the temporal C production - are similar for both modes of diffusion. However, the distinctive time scale for the non-Fickian case is very much larger even when the median transition steps are matched with the Fickian case. For immobile C, the spatial profile pattern is a broadening (Gaussian) reaction front evolving to a concentration-fluctuation dominated (Lorentzian) shape. The temporal C production is fit well by a stretched exponential for both diffusion types. In analyzing experiments, the appearance of a Gaussian C profile does not prove that the diffusion process is Fickian.

Original languageEnglish
Article number032812
Number of pages6
JournalPhysical Review B: covering condensed matter and materials physics
Volume87
Issue number3
DOIs
StatePublished - 25 Mar 2013

All Science Journal Classification (ASJC) codes

  • Statistical and Nonlinear Physics
  • Statistics and Probability
  • Condensed Matter Physics

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