Imbibition triggered by capillary condensation in nanopores

TL;DR

This study investigates how water is absorbed in nanoporous silicon through capillary condensation, revealing two distinct regimes of uptake and modeling the imbibition process with a modified Lucas-Washburn equation.

Contribution

The paper introduces a detailed experimental analysis of water uptake regimes in nanopores and proposes a modified Lucas-Washburn model incorporating Kelvin stresses.

Findings

Diffusion-like water uptake at low vapor saturation.

Fast imbibition front at high vapor saturation.

Modified Lucas-Washburn equation accurately describes imbibition dynamics.

Abstract

We study the spatio-temporal dynamics of water uptake by capillary condensation from unsaturated vapor in mesoporous silicon layers (pore radius $r_\mathrm{p} \simeq 2$ nm), taking advantage of the local changes in optical reflectance as a function of water saturation. Our experiments elucidate two qualitatively different regimes as a function of the imposed external vapor pressure: for low saturations, equilibration occurs via a diffusion-like process; for high saturations, an imbibition-like wetting front results in fast equilibration towards a fully saturated sample. We show that the imbibition dynamics can be described by a modified Lucas-Washburn equation that takes into account the liquid stresses implied by Kelvin equation.