When 20% Is Enough: Counterintuitive Contact Angle Maxima on Chemically Heterogeneous Hydrophobic/Hydrophilic...

Area of Science:

• Surface Science
• Materials Science
• Physical Chemistry

Background:

• Solid-liquid-gas systems are fundamental across scientific disciplines.
• Nanoscale phenomena in these systems are often explained by macroscopic laws.
• Atomic-scale surface features can significantly influence system behavior.

Purpose of the Study:

• To investigate the impact of atomic-scale chemical heterogeneities on hydrophobic surfaces.
• To explore counterintuitive behaviors in solid-liquid-gas three-phase systems.
• To understand the role of surface heterogeneity in contact line pinning.

Main Methods:

• Atomistic simulations were employed to model heterogeneous surfaces.
• Contact angles were analyzed for surfaces with varying hydrophilic particle concentrations and interaction forces.
• The pinning of the solid-liquid-gas contact line was investigated.

Main Results:

• Maximum contact angles were observed on hydrophobic surfaces with approximately 20% hydrophilic particles.
• Contact angle maxima also occurred when the interaction force difference between surface components reached around 40%.
• Atomistic heterogeneities were shown to effectively pin the solid-liquid-gas contact line.

Conclusions:

• Surface heterogeneities at the atomic scale can lead to counterintuitive wetting behaviors.
• These findings help explain the high hydrophobicity of materials with mixed hydrophilic/hydrophobic sites.
• The study highlights the limitations of asymptotic homogenization for describing complex heterogeneous surfaces.