First-passage approach for permeable traps

Many reactive processes in complex materials involve absorption of diffusing molecules. Recently, there has been interest in particle interaction with partially absorbing (or permeable) traps. Here, we present a simple and efficient method for accounting for the non-diffusion-limited reaction of particles when the flux of particles to the trap is governed by surface permeability. The trapping probability is determined from a one-dimensional Green's function, which results in a simple algebraic expression. This expression, which applies in the region immediately adjacent to the trap, is then used with a first-passage approach far from the trap. When applied to a suspension of permeable traps, the method is seen to give accurate results over the concentration range. The method is applied to the competition of reactive particles in a suspension of permeable spheres with a reactive continuous phase.