Capillary condensation between parallel walls of unequal length

Area of Science:

• Physics
• Physical Chemistry
• Materials Science

Background:

• Capillary condensation is crucial in porous materials and nanofluidics.
• Understanding condensation in confined geometries is essential for material design and function.

Purpose of the Study:

• To develop a macroscopic theory for capillary condensation in slits with unequal parallel walls.
• To identify distinct condensation states and their governing thermodynamic relations.

Main Methods:

• Macroscopic theory formulation.
• Introduction of the edge contact angle concept.
• Derivation of Kelvin-like relations for condensation onset.
• Analysis of phase diagrams based on wall geometry and contact angle.

Main Results:

• Identification of four distinct capillary condensation states.
• Discovery of a geometric separatrix dividing condensation regimes.
• Determination of a wedge-filling threshold at θ=π/4.
• Demonstration of geometry's role in onset and suppression of condensation.

Conclusions:

• The theory provides a framework for understanding capillary condensation in geometrically complex slits.
• Wall geometry and edge contact angle are key factors controlling condensation phenomena.
• The findings have implications for designing materials with controlled fluid adsorption properties.