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UBC Theses and Dissertations

Structure and properties of fluids near inert and metallic surfaces Bérard, Daniel Robert


General reductions of the Ornstein-Zernike equation are given for multicomponent molecular fluids near an isolated planar surface and between planar surfaces. This allows integral equation approximations such as the hypernetted-chain (HNC) and reference hypernetted-chain (RHNC) theories to be solved numerically. Theoretical methods for treating multipolar particles near inert, dielectric and metallic surfaces are considered. The metal is represented using a jellium model together with density-functional (DF) theory and the two phases interact electrostatically. Mean-field theories which reduce the many-body electrostatic wall-particle interactions to effective pair potentials are described for dielectric and metallic surfaces. The two interfacial phases are solved self-consistently for the wall-particle distribution function and, in the case of metal surfaces, for the electron density distributions. Explicit results are given for dipolar hard sphere fluids and for electrolyte solutions. The wall-induced fluid “structure”, electrostatic potential drop across the interface and electron density distribution of the metal are discussed in detail. Close to metallic surfaces, it is found that a highly ordered region exists. The dipoles are strongly ordered normal to the surface with the positive ends out. This is because the solvent structure effectively dictates the ion distributions near the surface. Hard sphere, Lennard-Jones and dipolar hard sphere fluids are investigated between inert walls. Lennard-Jones fluids are also considered between attractive walls. RHNC and HNC results for the fluid structure and the force acting between surfaces are compared with computer simulations. With the exception of Lennard-Jones fluids confined between inert walls, it is found that the integral equation theories show good agreement with simulation results. Integral equation and computer simulation results for Lennard-Jones fluids show better agreement as the distance of the state point from liquid-vapour bulk coexistence is increased. A detailed investigation of a Lennard-Jones fluid confined between inert walls using the grand canonical Monte Carlo method is performed. Capillary evaporation is found for liquid subcritical bulk states. General methods are given for simulating a metastable fluid. The force acting between the walls is found to be attractive and increases rapidly as the spinodal separation is approached. On the equilibrium liquid branch, the net pressure appears significantly more attractive than the van der Waals attraction at small separations. This might be the origin of the experimentally measured attraction between hydrophobic surfaces in water.

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