Lifetime of Surface Bubbles in Surfactant Solutions

Area of Science:

• Fluid Dynamics
• Surface Science
• Colloid and Interface Science

Background:

• Surface bubbles are common in nature and engineering, but surfactant effects on their residence time are unclear.
• Existing theoretical models often use lubrication theory, while experimental observations show bubbles approaching from a distance.
• A gap exists in understanding film drainage dynamics between bubbles and free surfaces, especially with surfactants.

Purpose of the Study:

• To bridge theoretical and experimental approaches to bubble-surface interactions.
• To investigate the coupled influence of bubble deformation and surfactants on rising and drainage processes.
• To provide a clearer understanding of film drainage phenomena beneath a free surface.

Main Methods:

• Direct numerical simulations using the level-set method for interface capturing.
• Solving the surfactant transport equation in an Eulerian framework.
• Axisymmetric simulations analyzing bubble acceleration, deformation, and drainage phases, varying Bond number (Bo) and Langmuir number (La).

Main Results:

• Surfactant-free interfaces show exponential decay in distance (h) between bubble and surface, faster for nondeformable bubbles (Bo ≪ 1).
• Surfactants (La > 0) reduce h decay: exponentially for large bubbles (Bo ≫ 1) and algebraically for small ones (Bo ≪ 1).
• Maximum bubble lifetime occurs near Bo ≈ 1, linked to interface Marangoni elasticity.

Conclusions:

• Bubble deformation and surfactant presence significantly alter film drainage dynamics.
• The study successfully integrates different approaches to bubble-surface interaction.
• Findings clarify the role of surfactants and bubble deformability in surface residence time.