Attractive forces between uncharged hydrophobic surfaces: direct measurements in aqueous solution

Area of Science:

• Surface science
• Physical chemistry
• Colloid and interface science

Background:

• Long, double-chained alkylammonium acetate surfactants adsorb onto muscovite mica.
• This adsorption forms electrically neutral, hydrophobic surfaces.

Purpose of the Study:

• Investigate attractive forces between hydrophobic surfaces.
• Determine the relationship between surface hydrophobicity and attractive forces.
• Understand the influence of water structure on these forces.

Main Methods:

• Adsorption of surfactants onto muscovite mica.
• Measurement of attractive forces between modified surfaces.
• Analysis of force decay behavior.

Main Results:

• Attractive forces are 10-100 times stronger than van der Waals forces up to 10 nm.
• Forces decay exponentially (proportional to exp(-D/1.4)), not by power-law.
• Force strength correlates with surface hydrophobicity.

Conclusions:

• Hydrophobic surface modification significantly enhances attractive forces.
• The long-range influence of surfaces on water structure drives these forces.
• Cavitation effects are observed for highly hydrophobic surfaces.