Capillary rise of water in hydrophilic nanopores

TL;DR

This study demonstrates that water rises in hydrophilic silica nanopores following classical laws, with a model accounting for strongly bound water layers and free water in the pore center, supported by experimental measurements.

Contribution

It introduces a model incorporating bound water layers and free water to explain capillary rise dynamics in silica nanopores, supported by experimental data.

Findings

Water imbibition follows Lucas-Washburn law in nanopores.

Bound water layers influence flow dynamics.

Experimental sorption data supports the two-component model.

Abstract

We report on the capillary rise of water in three-dimensional networks of hydrophilic silica pores with 3.5nm and 5nm mean radii, respectively (porous Vycor monoliths). We find classical square root of time Lucas-Washburn laws for the imbibition dynamics over the entire capillary rise times of up to 16h investigated. Provided we assume two preadsorbed strongly bound layers of water molecules resting at the silica walls, which corresponds to a negative velocity slip length of -0.5nm for water flow in silica nanopores, we can describe the filling process by a retained fluidity and capillarity of water in the pore center. This anticipated partitioning in two dynamic components reflects the structural-thermodynamic partitioning in strongly silica bound water layers and capillary condensed water in the pore center which is documented by sorption isotherm measurements.