Extent of Surface Force Additivity on Chemically Heterogeneous Substrates at Varied Orientations.

Area of Science:

• Surface Science
• Physical Chemistry
• Materials Science

Background:

• Surface interactions involve contributions from polar and hydrophobic moieties, which can be context-dependent.
• The Cassie additivity equation offers a framework for understanding wetting free energies on mixed surfaces.
• Understanding force additivity is crucial for predicting and designing the behavior of heterogeneous materials.

Purpose of the Study:

• To investigate the applicability of force additivity models for chemically mixed surfaces.
• To determine the molecular conditions influencing force additivity in heterogeneous systems.
• To provide guidelines for synthesizing novel materials with tailored properties in aqueous media.

Main Methods:

• Molecular dynamics and umbrella sampling simulations were employed.
• Simulations were performed on parallel and nonparallel mixed graphene surfaces with methyl and nitrile coatings.
• Analysis focused on the superposition of forces between homogeneous and heterogeneous surfaces.

Main Results:

• Superposition of forces provides a reasonable first-order approximation for interactions on mixed surfaces.
• Deviations from additivity are more pronounced in parallel configurations, with high hydrophobic content, and at small separations.
• Water polarizability did not significantly alter the observed interaction behavior.

Conclusions:

• Force additivity is a useful approximation for mixed surfaces, but deviations highlight the context dependence of hydrophobic interactions.
• The study identifies key molecular conditions for observing force additivity.
• Findings guide the design of new heterogeneous materials for aqueous applications.