The adsorption phenomenon of neutral particles from the limiting surfaces ofthe sample in the Langmuir approximation is investigated. The diffusionequation regulating the redistribution of particles in the bulk is assumed tobe of hyperbolic type, in order to take into account the finite velocity ofpropagation of the density variations. We show that in this framework thecondition on the conservation of the number of particles gives rise to anonlocal boundary condition. We solve the partial differential equationrelevant to the diffusion of particles by means of the separation of variables,and present how it is possible to obtain approximated eigenvalues contributingto the solution. The same problem is faced numerically by a finite differencealgorithm. The time dependence of the surface density of adsorbed particles isdeduced by means of the kinetic equation at the interface. The predictednon-monotonic behavior of the surface density versus the time is in agreementwith experimental observations reported in the literature, and is related tothe finite velocity of propagation of the density variations.
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