Adsorption-entanglement layers in flowing high molecular weight polymer solutions III: Solution concentration and solvent power

Adsorption entanglement layers are thick, i. e. multimolecular layers formed at solid surfaces during the flow of high molecular weight polymer solutions. The present publication is concerned with the influence of solution concentration and solvent power on the formation of these layers. Three polymers have been used, polyethylene, polymethylmethacrylate and atactic polystyrene in various solvents. The formation and thickness of layers were monitored from their effect on flow behaviour. Two flow geometries were used: Couette flow - where the layers cause peaks in the shear stress during continuous shearing, and capillary flow where the layers reduce the flow rate. The results indicate that there is a critical concentration below which no layers form, and that this critical concentration is an order of magnitude less than the conventionally defined overlap concentration. It is also deduced that the layers form more quickly, and grow to be thicker when better solvents are used.