Hydrodynamic slippage inferred from thin film drainage measurements in a solution of nonadsorbing polymer

Thin film drainage measurements are presented for submicron films of an "id eal elastic" or Boger fluid, which is a high molecular weight polymer solut ion in a high viscosity solvent. The measurements are made in a surface for ce apparatus, with the fluid being squeezed between two mica surfaces in a crossed cylinder geometry and the film thickness measured as a function of time to study its drainage behavior. No equilibrium surface forces are dete cted in this system, indicating that the polymer is nonadsorbing. The effec t of fluid elasticity is predicted to make drainage more rapid in a Boger f luid than for the equivalent Newtonian fluid. Qualitatively this is what is observed for films less than 600 nm thick, but the drainage is even more r apid than predicted for the elastic fluid. To account for this, it is sugge sted that slippage is occurring at the fluid-solid interfaces, and the data is analyzed in terms of a simple slip model. The slip length required to f it the data is in the range 30-50 nm. (C) 2000 American Institute of Physic s. [S0021-9606(00)71413-9].