Contact angles on surfaces using mean field theory: nanodroplets vs. nanoroughness

Area of Science:

• Surface science
• Nanotechnology
• Physical chemistry

Background:

• Understanding wetting behavior is crucial for nanoscale systems.
• Macroscopic models often fail at small length scales due to line tension and droplet size effects.

Purpose of the Study:

• To comprehensively examine lattice density functional theory (LDFT) on a pillared surface.
• To confirm LDFT's suitability for complex nanostructured surfaces.
• To investigate the failure of macroscopic models at the nanoscale.

Main Methods:

• Application of lattice density functional theory (LDFT).
• Simulation of fluid-wall interactions on a pillared surface.
• Comparison of LDFT results with off-lattice theories and macroscopic models.

Main Results:

• LDFT accurately reproduces qualitative changes in wetting behavior observed in other theories.
• The study reconciles apparently conflicting previous results by examining feature sizes comprehensively.
• LDFT demonstrates the failure of macroscopic models due to line tension and small droplet-to-feature size ratios.
• LDFT clearly shows the failure of macroscopic models when feature size is reduced.

Conclusions:

• LDFT is suitable for studying wetting on complex nanostructured surfaces.
• Macroscopic models fail on nanorough surfaces because surface-fluid interactions are not consistent across varying feature sizes.
• Macroscopic models do not accurately predict contact angles on nanorough surfaces for any droplet size.