An examination of the relation between the configurational stability of contained fluids and adsorption

The configurational stability of the contained fluid can be described by the difference in the Helmholtz free energies of the double and single interface configurations. The Helmholtz free energy is dependent on the shape of the liquid-vapour interface and the contact angle. Here the contact angle is shown to depend on adsorption. Using a water-glass system as a working model, three isotherms are studied to determine which best describes the adsorptive behaviour at near-saturation pressures. Next, an expression for the Helmholtz function difference which considers the local gravitational acceleration as an independent variable and incorporates the adsorption isotherm is developed. The resulting expression is examined to determine at what gravitational acceleration a system with known independent variables can be expected to make the transition from the single to the double interface configuration. For the temperatures and container diameters studied, the transitional g-level ranges over 0.0025 < g/g0 < 0.0035, where g0 = 9.806m/ s2.