Effects of molar mass, concentration and thermodynamic conditions on polymer-induced flow drag reduction

Drag reduction in Taylor flow of polystyrene solutions is investigated using a commercial rheometer equipped with a standard double-gap sample holder with axial symmetry. The dependence of drag reduction on various factors, including polymer molar mass, polymer concentration, and thermodynamic conditions is studied. Drag reduction induced by polystyrene in toluene is found to increase with increasing polymer concentration in the dilute concentration regime. It is also seen that molecules with high molar mass of the polymer promote drag reduction. In terms of hydrodynamic volume fraction normalisation, it is found that most of the drag reduction effect occurs at volume fractions below 0.2. It is observed that drag reduction is favoured by good thermodynamic conditions of the polymer-solvent system. Both the flow induced extension of the polymer chains and the hydrodynamic volume fraction occupied by the polymer molecules seem to play an important role for the drag reduction effect.