DRAINAGE OF THIN LIQUID-FILMS BETWEEN RELATIVELY SMOOTH SURFACES

Using a new surface force apparatus, static and dynamic measurements h ave been conducted to investigate the squeeze of a liquid from the con tact between a relatively smooth sphere and a plane. Simple liquids an d polymer melts (polyisoprene) have been studied, with different solid surfaces (mica, cobalt, gold, platinum, and steel). It has been found that an ''immobile'' layer of fluid is present on each solid surface which does not participate in the hydrodynamic flow of the liquid. The thickness of this film is relatively independent of the roughness of the solid, corresponds to a small number of molecular layers (I to 5), and is influenced by the structure of the molecule. These fluids show s two different behaviors: for small molecules the thickness of the '' immobile'' layer is proportional to the viscosity; for larger molecule s the thickness is proportional to the one-tenth power of the viscosit y. During the squeeze process, when the solid surfaces are close, a '' confined'' layer occurs due to molecule entanglement. This phenomenon is described for a semirigid hydrocarbon.