Bubbles nucleating on superhydrophobic micropillar arrays under flow

Area of Science:

• Surface science
• Fluid dynamics
• Materials science

Background:

• Supersaturated solutions flowing over microstructured hydrophobic surfaces typically induce bubble nucleation.
• Controlling this heterogeneous nucleation is essential for applications requiring stable hydrophobic surfaces.

Purpose of the Study:

• To investigate and control the heterogeneous nucleation of gas bubbles from supersaturated carbon dioxide (CO₂) solutions.
• To establish methods for achieving uniform nucleation patterns by manipulating surface topography and fluid flow.

Main Methods:

• Fabrication of microstructured hydrophobic surfaces with varying pillar shapes, sizes, and arrangements.
• Controlled flow of supersaturated CO₂ solution over the microstructured surfaces.
• Observation of nucleation using laser scanning confocal microscopy.
• Analysis of nucleation sites and bubble growth using numerical simulations.

Main Results:

• Uniform nucleation patterns were achieved by optimizing micropillar design and flow conditions.
• Nucleation was found to correlate with pressure drops behind micropillars, identified via numerical simulations.
• The direction of fluid flow influenced nucleation for round and triangular micropillars, but not square ones.
• Selective switching of nucleation on and off was demonstrated.

Conclusions:

• Micropillar geometry, size, and flow parameters offer precise control over heterogeneous gas bubble nucleation.
• Understanding these parameters is key to managing nucleation for applications like maintaining superhydrophobicity.
• The findings provide a pathway for replenishing gas layers essential for superhydrophobic surface functionality.