Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 201-212).Moving contact line problems involving polymeric materials and other complex fluids are encountered in many applications such as coating flows, gravity-driven drainage, and spin-coating operations. Viscous, capillary, inertial and gravitational forces can all be important in these flows depending on the scale and speed of the spreading process. In this research, a number of benchmark problems involving moving contact lines of viscous Newtonian and non-Newtonian polymeric fluids have been studied using non-invasive optical techniques. A detailed study of viscous Newtonian and non-volatile liquids spreading on smooth horizontal and inclined substrates is presented. A phase-modulated interference microscope was used to enable the simultaneous measurement of both the inner (microscopic) length scale and the outer (macroscopic) flow scale in addition to the intermediate matching region. The resulting measurements of both the apparent contact angle and lateral scale of the precursor wetting film agree quantitatively with theoretical predictions for the spreading of a van der Waals fluid over a wide range of capillary numbers (10-6 10) on a solid surface is also considered. Our experiments confirm the existence of a non-Newtonian 'foot' region in the vicinity of the moving contact line for highly entangled polymer melts. Our experimental results of the lateral and vertical scales of this 'foot' are in fair agreement with available theoretical predictions. The transient spreading motion of an ideal elastic 'Boger' fluid (consisting of a dilute solution of high molecular weight polymer dissolved in a viscous Newtonian solvent) is also investigated. It is shown that the spreading rate of this model elastic fluid is smaller than is observed for corresponding Newtonian fluid drops of similar size and viscosity due to the viscoelastic effects. A foot-like structure is detected at the leading edge of the droplet for these unentangled, elastic fluids as well ...by Hossein Pirouz Kavehpour.Ph.D
