Probing effective slippage on superhydrophobic stripes by atomic force microscopy

Area of Science:

• Fluid Dynamics
• Surface Science
• Materials Science

Background:

• Effective slippage of water on superhydrophobic surfaces is a known phenomenon.
• Experimental confirmation of theoretical predictions for this slippage has been lacking for over a decade.

Purpose of the Study:

• To experimentally validate theoretical predictions of water slippage on superhydrophobic surfaces.
• To develop and confirm a semi-analytical theory for hydrodynamic interactions with textured surfaces.

Main Methods:

• Measurement of drag force on a sphere approaching a superhydrophobic grooved plane.
• Application of a semi-analytical theory using the gas cushion model to determine local slip length.
• Comparison of experimental force-distance curves with analytical theories for homogeneous slipping planes.

Main Results:

• The effective slip length on superhydrophobic grooves was experimentally determined.
• At intermediate and large separations, the results agreed with theoretical predictions based on the fraction of gas sectors.
• At small separations, the effective slip length showed separation-dependent behavior, matching the developed semi-analytical theory.

Conclusions:

• The study provides the first experimental confirmation of theoretical predictions for effective slippage on superhydrophobic surfaces.
• The developed semi-analytical theory accurately models hydrodynamic interactions at various separations.
• The findings validate the use of the gas cushion model for predicting slip length on textured surfaces.