THIN LIQUID FILMS: MOLECULAR THEORY AND HYDRODYNAMIC IMPLICATIONS

A theory of thin liquid films (thin-films) and wetting is proposed which embraces molecular physics, statistical thermodynamics and continuum physics without imposing artificial distinctions.;When one fluid is slowly yet forcibly displaced by another from the vicinity of a solid surface, the interplay of disjoining pressure, capillarity and viscosity determines whether a residual film is left behind and whether there is an apparent three-phase contact line with a dynamic apparent contact angle. Disjoining pressure stems from the way intermolecular forces aggregate in submicroscopically thin films. A theory of fluid displacement in slots and tubes is put forward which adds disjoining pressure gradient to previous fluid mechanical analyses. It agrees well with experimental observations.;A likewise-founded theory of the spontaneous spreading of wetting liquids on solids is developed. It accounts for capillary pressure, gravitational potential, surface tension, and disjoining pressure gradients as driving forces for flow in thick thin-films and for surface diffusion of thin thin-films. The theory explains the effect of surface size on spreading of water drops on glass and the influence of surface tension gradients on the spreading of oils and other liquids on high-energy surfaces.;Equilibrium molecular theories of the microstructures of single-component fluids composed of simple nonpolar molecules at smooth homogeneous solids are investigated. When conditions are far enough from a critical point between bulk phases, a fluid-fluid meniscus can appear to intersect a solid with an angle of contact greater than 0(DEGREES) and less than 180(DEGREES). The theories predict that as conditions are changed so that the fluid pair approaches a critical point, one of the fluids becomes perfectly wetting at the interface between the solid and the other fluid, i.e., the apparent contact angle reaches 0(DEGREES) or 180(DEGREES). The transition from partial to complete wetting can occur any distance away from the critical point, and can be either a first- or second-order transition, depending on the relative strengths and ranges of fluid-fluid and fluid-solid interactions. The predictions of the theory accord with experiment.