# Self-Diffusion of Glycerol in $\gamma$-Alumina Nanopores: Understanding the Effect of Pore Saturation on the Dynamics of Confined Polyalcohols

## TL;DR

This study uses molecular dynamics simulations to explore how pore saturation affects glycerol's dynamics in $\gamma$-Al$_2$O$_3$ nanopores, revealing that interfaces significantly influence hydrogen bonding and fluid mobility.

## Contribution

It provides a detailed molecular-level understanding of how pore saturation and interfaces impact glycerol dynamics in confined geometries, clarifying previous conflicting observations.

## Key findings

- Solid/liquid interfaces slow glycerol dynamics due to hydrogen bonding.
- Liquid/gas interfaces reduce hydrogen bonds, increasing fluid mobility.
- Pore saturation conditions explain discrepancies in experimental results.

## Abstract

Molecular Dynamics simulations of glycerol confined in $\gamma$-Al$_2$O$_3$ slit nanopores are used to explain controversial and inconsistent observations reported in the literature regarding the dynamics of viscous fluids in confined geometries. Analysing the effects of the degree of confinement and pore saturation in this system, we found that the presence of the solid/liquid interface and the liquid/gas interface in partially saturated pores are the main contributors for the disruption of the hydrogen bond network of glycerol. Despite the reduction of hydrogen bonds between glycerol molecules caused by the presence of the solid, glycerol molecules near the solid surface can establish hydrogen bonds with the hydroxyl groups of $\gamma$-Al$_2$O$_3$ that significantly slow-down the dynamics of the confined fluid compared to the bulk liquid. On the other hand, the disruption of the hydrogen bond network caused by the liquid/gas interface in unsaturated pores reduces significantly the number of hydrogen bonds between glycerol molecules and results in a faster dynamics than in the bulk liquid. Therefore, we suggest that the discrepancies reported in the literature are a consequence of measurements carried out under different pore saturation conditions.