Adsorption-Induced Slip Inhibition for Polymer Melts on Ideal Substrates

摘要

Hydrodynamic slip of a liquid at a solid surface represents a fundamentalphenomenon in fluid dynamics that governs liquid transport at small scales. Forpolymeric liquids, de Gennes predicted that the Navier boundary conditiontogether with the theory of polymer dynamics imply extraordinarily largeinterfacial slip for entangled polymer melts on ideal surfaces; this Navier-deGennes model was confirmed using dewetting experiments on ultra-smooth,low-energy substrates. Here, we use capillary leveling - surface tension drivenflow of films with initially non-uniform thickness - of polymeric films onthese same substrates. Measurement of the slip length from a robustone-parameter fit to a lubrication model is achieved. We show that at the lowershear rates involved in leveling experiments as compared to dewetting ones, theemployed substrates can no longer be considered ideal. The data is insteadconsistent with physical adsorption of polymer chains at the solid/liquidinterface. We extend the Navier-de Gennes description using one additionalparameter, namely the density of physically adsorbed chains per unit surface.The resulting formulation is found to be in excellent agreement with theexperimental observations.