How closely can a solid approach an air-water surface without becoming wet?

Area of Science:

• Physics
• Physical Chemistry
• Surface Science

Background:

• Understanding object interaction with fluid interfaces is crucial in various scientific and engineering fields.
• The van der Waals force plays a significant role in phenomena occurring at interfaces.
• Previous studies have explored surface interactions but lacked a definitive limit for object approach.

Purpose of the Study:

• To investigate the limiting height an object can approach an air-water interface.
• To understand the interplay between van der Waals forces, buoyancy, and surface tension.
• To derive a practical formula for this absolute limiting height.

Main Methods:

• Numerical simulation of interface shape under van der Waals interaction.
• Analysis of governing equations to determine solvability limits.
• Derivation of a closed-form expression for the limiting height.

Main Results:

• Identified two key length scales governing interface deformation: one for van der Waals forces and one for buoyancy/surface tension.
• Developed a closed-form expression for the absolute limiting height.
• The formula depends solely on the Hamaker constant and the solid's geometry.

Conclusions:

• The study provides a fundamental understanding of object-interface proximity limits.
• The derived formula offers a practical tool for predicting approach limits.
• This work advances the knowledge of interfacial physics and van der Waals interactions.