"Spreading Kinetics of Constrained Thin Films"
The rate at which a liquid spreads over a solid surface is called the wetting kinetics, which deals with the rates at which a liquid moves over a solid surface and displaces a second fluid. Since the liquid film thickness gradually decreases to zero as the contact line, the line common to the solid-liquid-vapor phases, is approached, the special properties of thin liquid films play an important role. Of importance here is the disjoining pressure, which is related to the excess potential in thin films (less than 100 nanometers), and can be used as a body force to describe the hydrodynamics and equilibrium. This analytical research is for a liquid that has both attraction and repulsion for the solid substrate in its disjoining pressure, which is common but has not been analyzed. Although the thin film phenomenon determines that the liquid is non-wetting, the dynamics of spreading itself seems unaffected in the experiments by the disjoining pressure until the time when the moving liquid suddenly equilibrates. A quantitative description of how such a behavior arises will be made clear from the results of this research. The fluid mechanical equations for the profile of the moving liquid film will be solved numerically. The numerical method is made very difficult by the need to look at two very different length scales, the scale of the basic liquid mass and the thin film dimensions, and over very long times. Additionally, the effect of liquid evaporation and surface roughness will be considered, since they bring in great deal of reality to the analysis.