Bridging scales in disordered porous media by mapping molecular dynamics onto intermittent Brownian motion

C Bousige and P Levitz and B Coasne, NATURE COMMUNICATIONS, 12, 1043 (2021).

DOI: 10.1038/s41467-021-21252-x

Owing to their complex morphology and surface, disordered nanoporous media possess a rich diffusion landscape leading to specific transport phenomena. The unique diffusion mechanisms in such solids stem from restricted pore relocation and ill-defined surface boundaries. While diffusion fundamentals in simple geometries are well-established, fluids in complex materials challenge existing frameworks. Here, we invoke the intermittent surface/pore diffusion formalism to map molecular dynamics onto random walk in disordered media. Our hierarchical strategy allows bridging microscopic/mesoscopic dynamics with parameters obtained from simple laws. The residence and relocation times - t(A), t(B)- are shown to derive from pore size d and temperature-rescaled surface interaction epsilon/k(B)T. t(A) obeys a transition state theory with a barrier similar to epsilon/k(B)T and a prefactor -10(-12)s corrected for pore diameter d. t(B) scales with d which is rationalized through a cutoff in the relocation first passage distribution. This approach provides a formalism to predict any fluid diffusion in complex media using parameters available to simple experiments.

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