Capillary condensation between parallel walls of unequal length

TL;DR

This paper develops a macroscopic theory for capillary condensation between parallel walls of unequal length, revealing how geometry influences condensation states and thresholds through phase diagrams and Kelvin-like relations.

Contribution

It introduces the concept of an edge contact angle and derives phase diagrams showing how geometry controls condensation regimes and thresholds.

Findings

Identification of four distinct condensation states.

Derivation of Kelvin-like relations for condensation onset.

Discovery of a wedge-filling threshold at b8=a0/4.

Abstract

We present a macroscopic theory of capillary condensation in slits formed by parallel walls of unequal length. Using the concept of an edge contact angle, we identify four distinct condensation states and derive Kelvin-like relations for their onset. The resulting phase diagrams, expressed in terms of wall geometry and contact angle, reveal two central organizing features: a geometric separatrix that divides distinct condensation regimes, and the wedge-filling threshold at $\theta=\pi/4$, which separates a rich four-state scenario from a simpler two-state one. These results demonstrate how geometry dictates the onset and suppression of condensation in confined systems.