Understanding the asymmetry between advancing and receding microscopic contact angles.

Area of Science:

• Fluid dynamics
• Interfacial science
• Computational physics

Background:

• Microscopic dynamic contact angles are crucial for understanding fluid behavior at interfaces.
• Previous studies often simplified the complex dynamics at moving contact lines.
• Unequal wettability between fluids and solid surfaces can lead to anisotropic interfacial phenomena.

Purpose of the Study:

• To analyze advancing and receding microscopic contact angles in a shear flow of two mono-atomic fluids confined between solid walls.
• To investigate the influence of asymmetric fluid density changes on dynamic contact angles.
• To determine the relationship between contact line velocity and differing advancing/receding angles.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model the fluid system.
• The instantaneous interface method was used to define microscopic dynamic contact angles based on fluid density distributions.
• Analysis focused on shear flow conditions between parallel non-polar solid walls.

Main Results:

• Asymmetric fluid density changes near the wall were observed with respect to the moving contact line.
• A distinct dependence of advancing and receding contact angles on contact line velocity was found when fluid wettability was unequal.
• This difference in contact angles leads to varied flow resistance at advancing and receding contact lines.

Conclusions:

• The asymmetry in microscopic dynamic contact angles is driven by unequal fluid wettability and density distribution.
• The differing flow resistance associated with advancing and receding contact lines has implications for microfluidic devices.
• Findings highlight the importance of considering dynamic contact angle asymmetry in industrial fluid transport applications.