Cell dynamics simulation of droplet and bridge formation within striped nano-capillaries

TL;DR

This study uses a TDGL-type model to simulate droplet and bridge formation in striped nano-capillaries, revealing the influence of substrate potential and confirming classical condensation scenarios.

Contribution

It introduces a two-dimensional, noise-included TDGL model to simulate nano-scale droplet and bridge dynamics within chemically heterogeneous capillaries.

Findings

Morphology evolution from droplet to bridge is visualized.

Substrate potential critically influences nanoscopic bridge morphology.

Capillary condensation dynamics are nearly temperature-independent.

Abstract

The kinetics of droplet and bridge formation within striped nano-capillaries is studied when the wetting film grows via interface-limited growth. The phenomenological time-dependent Ginzburg-Landau (TDGL)-type model with thermal noise is used and numerically solved using the cell dynamics method. The model is two-dimensional and consists of undersaturated vapor confined within a nano-capillary made of two infinitely wide flat substrates. The surface of the substrate is chemically heterogeneous with a single stripe of lyophilic domain that exerts long-range attractive potential to the vapor molecule. The dynamics of nucleation and subsequent growth of droplet and bridge can be simulated and visualized. In particular, the evolution of the morphology from droplet or bump to bridge is clearly identified. Crucial role played by the substrate potential on the morphology of bridge of nanoscopic size is clarified. Nearly temperature-independent evolution of capillary condensation is predicted when the interface-limited growth dominates. In addition, it is shown that the dynamics of capillary condensation follows the scenario of capillary condensation proposed by Everett and Haynes three decades ago.