Equilibrium Contact Angle and Adsorption Layer Properties with Surfactants

Area of Science:

• Physical Chemistry
• Surface Science
• Fluid Dynamics

Background:

• The Young equation relates interfacial energies to macroscopic contact angles.
• Mesoscale wettability is modeled using film-height-dependent wetting energy.
• Consistency between macro- and mesoscale descriptions requires a specific relation between interface energy and adsorption layer thickness.

Purpose of the Study:

• To derive a consistency condition between macroscopic and mesoscopic descriptions for a liquid-surfactant system.
• To investigate the impact of insoluble surfactants on contact line equilibrium and wetting energy.
• To establish a relationship between wetting energy and surfactant concentration.

Main Methods:

• Derivation of macroscopic and mesoscopic descriptions for a contact line with insoluble surfactants.
• Development of a consistency condition linking wetting energy to surfactant concentration.
• Theoretical analysis and comparison with time-dependent numerical simulations.

Main Results:

• A novel consistency condition for wetting energy dependence on surfactant concentration was derived.
• The study demonstrates that surfactant inhomogeneity at equilibrium leads to a non-trivial contact angle dependence on concentration.
• Excellent agreement was found between theoretical predictions and numerical simulations for dilute surfactants.

Conclusions:

• The derived consistency condition ensures macroscopic and mesoscopic descriptions align for liquid-surfactant systems.
• Wetting behavior is significantly influenced by the spatial distribution of insoluble surfactants.
• The findings provide a theoretical framework for understanding and predicting contact line phenomena in the presence of surfactants.