A partial equilibrium theory for liquids bonded to immobile solids

Area of Science:

• Physical Chemistry
• Surface Science
• Thermodynamics

Background:

• The Young-Laplace (YL) theory quantitatively predicts capillary rise based on contact angles and surface tension.
• Gibbs's work related chemical potentials to interface free energies for consistency with YL theory.
• Existing theories assume equilibrium chemical potentials are identical in bulk and interface phases.

Purpose of the Study:

• To evaluate postulates for partial equilibrium (PE) states of liquids at interfaces with solids.
• To investigate the role of solid surface attractive fields versus meniscus curvature in capillary rise.
• To develop a theory consistent with experimental observations of capillary phenomena.

Main Methods:

• Evaluation of two postulates regarding partial free energies and equilibrium chemical potentials at interfaces.
• Derivation of partial equilibrium (PE) equations for drops, films, and liquids.
• Experimental measurement of contact angles for water on glass and Teflon surfaces.

Main Results:

• PE equations predict capillary rise height and condensate volume similarly to YL theory and Kelvin equation, respectively.
• Experimental contact angle measurements contradict YL assumptions about meniscus angles.
• PE theory identifies solid surface attraction, not meniscus curvature, as the primary driver of capillary rise.
• PE theory accurately fits experimental data for divergent water films on quartz for thicknesses > 1.5 nm.

Conclusions:

• Partial equilibrium theory provides a more accurate framework for understanding capillary phenomena than Young-Laplace theory.
• Solid surface attractive fields play a crucial role in capillary rise and film formation.
• PE theory offers a unified approach to capillary phenomena, including film divergence/convergence and interactions with strain.