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

• Published in: Nature communications Vol. 12; no. 1; p. 1043
• Main Authors: Bousige, Colin, Levitz, Pierre, Coasne, Benoit
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 15.02.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 639/301/357; 639/638/440; 639/638/563/980; 639/638/563/981; Brownian motion; Chemical Sciences; Complex media; Computational fluid dynamics; Condensed Matter; Diffusion; Fluid dynamics; Formalism; Humanities and Social Sciences; Materials Science; Molecular dynamics; Morphology; multidisciplinary; or physical chemistry; Parameters; Physics; Pore size; Porosity; Porous media; Random walk; Relocation; Science; Science (multidisciplinary); Simulation; Theoretical and; Transport phenomena
• ISSN: 2041-1723; 2041-1723
• 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 ε / k B T . t A obeys a transition state theory with a barrier ~ ε / 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. The diffusion of fluids in complex nanoporous geometries represents a challenge for modelling approaches. Here, the authors describe the macroscopic diffusivity of a simple fluid in disordered nanoporous materials by bridging microscopic and mesoscopic dynamics with parameters obtained from simple physical laws.