Variation of the Hydrodynamic Polymer Layer Thickness on Solid Surfaces with Molecular Weight and Concentration

An extensive study on the determination of the 'hydrodynamic' layer thickness of polymer solutions and melt polymers was conducted with a surface force apparatus. For different concentrations and polymer molecular weights, a 'hydrodynamic layer' of fluid was detected on each solid surface which did not contribute to the flow. These thicknesses, denoted as LH, are compared to the characteristic polymer dimensions and the hydrodynamic (R H ) and gyration (R g ) radii. It appears that in contrast to the molecular weight, polymer concentration has little effect on the relative hydrodynamic layer thickness (L H /2R H , L H /2R g ). Indeed, this ratio indicates that two coils of low molecular weight and one coil of high molecular weight are 'immobile' on the solid surfaces. The mechanism responsible could be entanglement of the free (unattached) chains in the bulk with immobilized chains on the surface.