Wagging the contact line: transverse and longitudinal waves.

Area of Science:

• Fluid dynamics
• Surface science
• Physical chemistry

Background:

• Wetting phenomena are crucial in various scientific and industrial applications.
• Understanding contact line dynamics, especially on non-ideal surfaces, is essential.
• Previous studies often focused on idealized smooth surfaces.

Purpose of the Study:

• To investigate the kinetics of wetting on rough surfaces.
• To analyze the effects of imposed longitudinal or transverse oscillations on the contact line.
• To identify and interpret instabilities during wetting on rough surfaces.

Main Methods:

• Experimental investigation of wetting kinetics.
• Imposing small-amplitude oscillations on the contact line.
• Analysis of viscous dissipation during spreading on a model rough surface.

Main Results:

• Observed steady spreading with superimposed longitudinal or transverse oscillations.
• Small effects of imposed motion attributed to low spreading rates and dynamic contact angles.
• A singularity in viscous dissipation was identified on the rough surface.

Conclusions:

• The observed viscous dissipation singularity suggests an instability during wetting on rough surfaces.
• This instability is analogous to Haines' jumps and stick-slip phenomena.
• Potential for fluid entrainment during these instabilities was noted, linking previously unconnected phenomena.