Effects of Pore Connectivity and Tortuosity on the Dynamics of Fluids Confined in Sub-nanometer Pores

TL;DR

This study uses molecular dynamics simulations to explore how pore connectivity and tortuosity in silicalite influence the translational, rotational, and vibrational dynamics of CO₂ and ethane, revealing nuanced effects relevant for fluid separation.

Contribution

It provides a detailed molecular-level analysis of how pore connectivity and tortuosity affect fluid dynamics in nanoporous materials, which was previously not well understood.

Findings

Pore connectivity enhances both translational and rotational fluid motions.

Pore tortuosity facilitates rotational but suppresses translational motion of CO₂.

Vibrational modes shift to higher energies with increased pore tortuosity.

Abstract

We report molecular dynamics simulation studies addressing the effects of pore connectivity on the dynamics of two representative fluids CO$_2$ and ethane in silicalite by systematically varying the degree of pore connectivity through selectively blocking some pore space with immobile methane molecules. By selectively turning off the pore spaces in the shape of straight, or tortuous zigzag channels, we also probe the effects of pore tortuosity. In general, pore connectivity is found to facilitate both the translational as well as rotational dynamics of both fluids, while the intermolecular modes of vibration in both fluids remain largely unaffected. The effects of providing connections between a set of straight or zigzag channel-like pores are however more nuanced. Pore tortuosity facilitates the rotational motion, but suppresses the translational motion of CO$_2$, while its effects on the rotational and translational motion of ethane are less pronounced. The intermolecular vibrational modes of both fluids shift to higher energies with an increase in the number of tortuous pores. The results reported here provide a detailed molecular level understanding of the effects of pore connectivity on the dynamics of fluids and thus have implications for applications like fluid separation.