Contact Line Motion over a Surface Asperity: Jumping and Energy Dissipation

Area of Science:

• Physics
• Materials Science
• Surface Science

Background:

• Understanding wetting dynamics and contact angle hysteresis on real surfaces requires knowledge of moving contact line interactions with surface defects.
• Atomic force microscopy (AFM) experiments often involve cylindrical fiber geometries where such interactions are relevant.

Purpose of the Study:

• To investigate how isolated topographical defects influence contact line motion on a cylindrical fiber.
• To analyze the quasistatic force-displacement behavior of a meniscus over nanoscale bumps.
• To quantify energy dissipation during pinning and depinning events.

Main Methods:

• Numerical simulations of a meniscus advancing and receding over a single nanoscale bump on a cylindrical fiber.
• Analysis of force-displacement curves to identify pinning and depinning jumps.
• Development of approximated expressions for dissipated energy.

Main Results:

• Distinct pinning and depinning jumps of the contact line were observed, leading to dissipated energy.
• Depinning dissipated energy was found to be larger than pinning dissipated energy, with most dissipation occurring during depinning.
• Approximated expressions for dissipated energy showed good agreement with simulations and AFM experiments.
• Simulations of pits and chemical heterogeneities revealed different signatures in force curves.
• Contact line jumps were found to occur near the velocity of capillary waves.

Conclusions:

• The study provides fundamental insights into contact angle hysteresis and energy dissipation mechanisms in wetting phenomena.
• The developed model accurately predicts dissipated energy, correlating simulation and experimental results.
• The findings are crucial for understanding wetting on real-world surfaces with topographical and chemical variations.