Crossover from anomalous to normal diffusion in porous media

摘要: Random walks (RW) of particles adsorbed in the internal walls porous deposits produced by ballistic-type growth models are studied. The start at external surface and enter their pores order to simulate an flux a species towards solid. For short times, walker concentration decays as stretched exponential depth z, but crossover long-time normal diffusion is observed most samples. anomalous profile remains long times very solids if steps restricted nearest neighbors accompanied with subdiffusion features. These findings correlated decay explored area z. study RW tracer left part solid rules out interpretation equations position-dependent coefficients. A model tube decreasing cross section explains those results showing crossovers from effective regime asymptotic diffusion. position density analytically calculated for exponentially z show good agreement numerical data. interpreted templating effect shape on total number diffusing each depth, while volumetric actually region may not have significant decay. explain metal atoms recent works. They also confirm difficulty interpreting experimental or computational data transport reported works, particularly only profiles measured.