Tagged-particle dynamics in a fluid adsorbed in a disordered porous solid: interplay between the diffusion-localization and liquid-glass transitions

TL;DR

This paper develops a mode-coupling theory for single-particle dynamics in fluids within disordered porous media, revealing how confinement strength influences diffusion-localization and glass transitions, with distinct scenarios for weak and strong confinement.

Contribution

It introduces a new theoretical framework that extends previous models to include the effects of confinement on single-particle and collective dynamics in disordered porous solids.

Findings

Weak confinement leads to a discontinuous diffusion-localization transition coinciding with the glass transition.

Strong confinement results in a continuous transition occurring before the collective dynamics become nonergodic.

Multiple types of glass transitions, including secondary transitions, are identified near the dynamical arrest points.

Abstract

A mode-coupling theory for the slow single-particle dynamics in fluids adsorbed in disordered porous media is derived, which complements previous work on the collective dynamics [V. Krakoviack, Phys. Rev. E 75, 031503 (2007)]. Its equations, like the previous ones, reflect the interplay between confinement-induced relaxation phenomena and glassy dynamics through the presence of two contributions in the slow part of the memory kernel, which are linear and quadratic in the density correlation functions, respectively. From numerical solutions for two simple models with pure hard core interactions, it is shown that two different scenarios result for the diffusion-localization transition, depending on the strength of the confinement. For weak confinement, this transition is discontinuous and coincides with the ideal glass transition, like in one-component bulk systems, while, for strong confinement, it is continuous and occurs before the collective dynamics gets nonergodic. In the latter case, the glass transition manifests itself as a secondary transition, which can be either continuous or discontinuous, in the already arrested single-particle dynamics. The main features of the anomalous dynamics found in the vicinity of all these transitions are reviewed and illustrated with detailed computations.