A novel approach to interpretation of the time-dependent self-diffusion coefficient as a probe of porous media geometry

[Display omitted] ► New approximation describing fluid diffusion in the porous media. ► Time dependence of the self-diffusion coefficient. ► Choosing semi-log coordinates can reduce the time dependence to linear. ► Slope determined by the porous media geometry and the bulk self-diffusion coefficient. This article presents a new approximation describing fluid diffusion in porous media. Time dependence of the self-diffusion coefficient D(t) in the permeable porous medium is studied based on the assumption that diffusant molecules move randomly. An analytical expression for time dependence of the self-diffusion coefficient was obtained in the following form: D(t)=(D0-D∞)exp(-D0t/λ)+D∞, where D0 is the self-diffusion coefficient of bulk fluid, D∞ is the asymptotic value of the self-diffusion coefficient in the limit of long time values (t→∞), λ is the characteristic parameter of this porous medium with dimensionality of length. Applicability of the solution obtained to the analysis of experimental data is shown. The possibility of passing to short-time and long-time regimes is discussed.