Critical-point wedge filling and critical-point wetting

Area of Science:

• Surface science
• Adsorption phenomena
• Thermodynamics

Background:

• Critical-point wetting, the vanishing contact angle at T_w < T_c, is not guaranteed for fluids on planar substrates.
• Imbalances in the range of wall-fluid vs. fluid-fluid forces can lead to nonwetting gaps in surface phase diagrams.

Purpose of the Study:

• To demonstrate that fluids in wedges (and cones) always exhibit critical-point filling, irrespective of force range imbalances.
• To investigate critical-point filling in the absence of critical-point wetting.

Main Methods:

• Utilized a microscopic density functional theory model for fluid adsorption in a right-angle wedge.
• Incorporated dispersion and retarded dispersion-like wall-fluid forces.
• Determined the location and order of filling phase boundaries.

Main Results:

• Confirmed that critical-point filling (wedge wetting/drying) occurs universally in wedges due to converging contact angle lines at T_c.
• The model results showed excellent agreement with thermodynamic requirements and interfacial model predictions for critical singularities.

Conclusions:

• Critical-point filling is a robust phenomenon in confined geometries like wedges, even when planar wetting fails.
• The study validates theoretical predictions and provides a microscopic understanding of adsorption in wedges.