Pore opening effects and transport diffusion in the Knudsen regime in comparison to self- (or tracer-) diffusion

TL;DR

This study investigates molecular diffusion in nanopores within the Knudsen regime, demonstrating that transport and self-diffusion coefficients are equal when accounting for pore roughness, refining previous models.

Contribution

The paper introduces an extended calculation method showing equality of self- and transport diffusion coefficients in the Knudsen regime, considering pore roughness effects.

Findings

Transport and self-diffusion coefficients are equal in the Knudsen regime.

The extended method improves accuracy over previous models.

Pore roughness does not affect the equality of diffusion coefficients.

Abstract

We study molecular diffusion in linear nanopores with different types of roughness in the so-called Knudsen regime. Knudsen diffusion represents the limiting case of molecular diffusion in pores, where mutual encounters of the molecules within the free pore space may be neglected and the time of flight between subsequent collisions with the pore walls significantly exceeds the interaction time between the pore wall and the molecules. We present an extension of a commonly used procedure to calculate transport diffusion coefficients. Our results show that using this extension, the coefficients of self- and transport diffusion in the Knudsen regime are equal for all regarded systems, which improves previous literature data.