A hard sphere fluid with quantum correction in nanospherical pores: A DFT study

Abstract

In this paper, the density functional theory is employed, drawing upon the effective diameter method, to investigate the effects of quantum correction on the structure and such thermodynamic properties of quantum-mechanical hard sphere fluids confined in nano-scale spherical cavities as excess adsorption, interfacial tension, solvation force, and local normal pressure. Results indicate that quantum correction performed on the modified fundamental measure theory yields accurate results for hard sphere fluids. It is also found that the repulsion between quantum-mechanical hard sphere molecules before they come into contact play an important role in determining the structure and thermodynamic properties of the confined fluid. The periodic oscillation in the density profile becomes more obvious and the order of layers in the pore increases as a result of increased quantum effect, λ⁎. Increasing the values of λ⁎ is found to lead not only to increased excess adsorption of the fluid confined in pores but also to drastic changes in the structure of the fluid molecules, thereby increasing the interfacial tension. Another finding of the present study involves the failure of the quantum correction to change either the sign or the qualitative behavior of interfacial tension and excess adsorption with curvature. In the quantum mechanical fluid, pressure arises from collisions without direct contact, that is, from inter-particle repulsions. It is observed that the quantum-mechanical repulsions become great, the periodic oscillation in the pressure profile becomes more obvious, and pressure grows larger at extremely low temperatures and high densities. Investigation of the quantum mechanical molecules escaping repulsion revealed their greater tendency for accumulation at the pore wall; hence, the higher normal pressure and wall pressure at the pore wall.