Intrusion and extrusion of water in hydrophobic mesopores

TL;DR

This study combines experimental and theoretical approaches to understand water intrusion and extrusion in hydrophobic mesopores, highlighting the role of capillary effects and vapor bubble nucleation with line tension considerations.

Contribution

It provides a detailed analysis of intrusion-extrusion cycles in hydrophobic mesopores, emphasizing the importance of line tension in vapor bubble nucleation during extrusion.

Findings

Intrusion can be modeled with macroscopic capillary theory.

Extrusion involves vapor bubble nucleation influenced by line tension.

Negative line tensions of about 10^{-11} J/m are observed.

Abstract

We present experimental and theoretical results on intrusion-extrusion cycles of water in hydrophobic mesoporous materials, characterized by independent cylindrical pores. The intrusion, which takes place above the bulk saturation pressure, can be well described using a macroscopic capillary model. Once the material is saturated with water, extrusion takes place upon reduction of the externally applied pressure; Our results for the extrusion pressure can only be understood by assuming that the limiting extrusion mechanism is the nucleation of a vapour bubble inside the pores. A comparison of calculated and experimental nucleation pressures shows that a proper inclusion of line tension effects is necessary to account for the observed values of nucleation barriers. Negative line tensions of order $10^{-11} \mathrm{J.m}^{-1}$ are found for our system, in reasonable agreement with other experimental estimates of this quantity.