Impact of small-scale geometric roughness on wetting behavior

Area of Science:

• Surface science
• Fluid dynamics
• Materials science

Background:

• Understanding fluid behavior on rough surfaces is crucial for various applications.
• Existing models often assume macroscopic roughness, neglecting molecular-scale effects.

Purpose of the Study:

• To investigate how small-scale geometric substrate roughness influences fluid wetting.
• To determine the critical length scale at which macroscopic wetting models become unreliable.

Main Methods:

• Utilized molecular simulation to create roughness wetting diagrams.
• Analyzed contact angle progression across Cassie, Wenzel, and impregnation regimes.
• Varied substrate feature periodicity to observe effects on wetting behavior.

Main Results:

• Wetting diagrams deviate from common curves as feature size approaches 10 fluid diameters.
• Macroscopic Cassie and Wenzel models lose reliability at this scale.
• Confinement effects and evolving substrate-fluid interactions explain deviations.

Conclusions:

• Substrate roughness at the molecular scale fundamentally alters fluid wetting.
• Macroscopic models are inadequate for predicting wetting on nanoscale rough surfaces.
• Confinement and interaction strength are key factors in nanoscale wetting phenomena.