Universal Repulsive Contribution to the Solvent-Induced Interaction Between Sizable, Curved Hydrophobes

Area of Science:

• Physical Chemistry
• Colloid and Surface Science
• Nanotechnology

Background:

• Hydrophobic surfaces in water experience attractive forces mediated by interfacial water.
• Understanding these forces is crucial for controlling nanoparticle behavior in aqueous environments.

Purpose of the Study:

• To identify conditions where water-induced interactions between curved hydrophobic surfaces become repulsive.
• To investigate the role of interfacial water in nanoparticle interactions.
• To enhance predictions of wetting and dispersion for nonpolar nanoparticles.

Main Methods:

• Geometric arguments to derive conditions for repulsive interactions.
• Mean-field approach augmented with atomistic simulations.
• Simulations of graphitic nanoparticles (spherical, cylindrical, planar) in water.

Main Results:

• Identified thermodynamic penalty from liquid/vapor boundary emergence as the source of repulsion.
• Demonstrated macroscopic thermodynamic principles apply at the molecular scale for nanoparticle interactions.
• Showcased applicability across spherical, cylindrical, and planar geometries.

Conclusions:

• Water-induced interactions between hydrophobic surfaces can be repulsive under specific geometric conditions.
• The study bridges macroscopic thermodynamics and molecular-scale phenomena in hydrophobic interactions.
• Provides a framework for improved control over nanoparticle wetting and dispersion.