MODELING OF COALESCENCE AND MEASURING SURFACE SHEAR VISCOSITY

This thesis consists of four chapters.;In Chapter II the coalescence time and rupture thickness of a draining film between a small drop or bubble and a fluid-fluid interface are estimated from expressions for the thinning rate at the rim of the film. The effects of a negative van der Waals disjoining pressure are considered. Predictions are compared with data of Allen et al. (1961) for single small nitrogen bubbles approaching an air-liquid interface.;In Chapter III the thinning of a dimpled liquid film as a large drop or bubble approaches a horizontal solid plane is studied by modifying Lin and Slattery's (1982) theory for a small drop or bubble approaching a solid plane. A family of solutions are found. Each of these solutions corresponds to a different radical position where the pressure in the draining film approaches the local hydrostatic pressure. Further study is suggested for the effects of gravity in the draining film.;In Chapter IV the surface stress-deformation behavior of the interface between air and 0.1 wt% aqueous solution of dodecyl sodium sulfate is studied by measuring the velocity distribution in the interface with a deep-channel surface viscometer. The surface shear viscosity of this system is found to be a function of surface rate of deformation. The results are compared with those measured by Jiang (1982) using rotational surface viscometers in our laboratory. Comparison of the results shows that the surface shear viscosity is not just some adjustable parameter required to obtain agreement between theory and experiment, but has instead a physical meaning.;In Chapter I Lin and Slattery's (1982) theory for the thinning of a dimpled liquid film as a small drop or bubble approaches a horizontal solid plane is extended to include the effects of London-van der Waals forces. Given only the drop or bubble radius and the required physical properties, the evolution of the film profile can be described. A positive van der Waals disjoining pressure retards the thinning at the rim and results in the formation of a flat liquid film. A negative van der Waals disjoining pressure enhances the thinning at the rim and results in the rupture of the liquid film in a finite time. Predictions of the present theory, Lin and Slattery's (1982) theory, and Frankel and Mysels' (1962) theory are compared with data for three systems exhibiting positive disjoining pressure studied by Platikanov (1964).