Systematically altering the hydrophobic nanobubble bridging capillary force from attractive to repulsive

Area of Science:

• Surface science
• Colloid science
• Nanotechnology

Background:

• Hydrophobic surfaces can form nanobubbles in aqueous solutions.
• Nanobubbles can mediate long-range forces between surfaces.
• Ethanol-water mixtures alter solution properties like surface tension.

Purpose of the Study:

• To investigate the effect of ethanol/water concentration on nanobubble bridging capillary forces.
• To understand how these forces change with varying ethanol concentrations.
• To determine the parameters influencing capillary forces in ethanol-water mixtures.

Main Methods:

• Atomic Force Microscopy (AFM) was employed to measure forces.
• Nanobubbles were generated on hydrophobic silica surfaces using solvent-exchange and surface scanning.
• A capillary force model was used to analyze the experimental data.

Main Results:

• In pure water, a strong, long-range attractive force (approx. 230 nm) was observed.
• Increasing ethanol concentration reduced the magnitude of the attractive force.
• At 40% ethanol by mass, the force became repulsive; above this, capillary forces vanished.

Conclusions:

• Ethanol concentration significantly alters nanobubble capillary forces between hydrophobic surfaces.
• The study provides insights into the role of solvent composition in interfacial forces.
• The findings are explained by changes in bridge geometry, contact angle, and volume.