| Abstract: | A reduction of frictional drag in turbulent flow was obtained in benzene by using three monodisperse polystyrene samples having weight-average molecular weights of 1.8, 4.1 and 7.1 × 106. By testing these polymers individually and in mixtures, data were obtained for samples with known molecular weight distributions. The drag reduction of these samples was studied as a function of polymer concentration and flow rate so that a generalized picture of the effects of polydispersity could be obtained. These results are used to help explain much of the behavior that was observed for polystyrene and other polymers. This includes the fact that the polystyrene samples exhibit a remarkably high resistance to the loss of drag reduction via degradation in turbulent flow. Such experiments indicate that drag reduction and degradation depend strongly on molecular weight distribution. Thus a molecular level interpretation of experimental results cannot be made unless the effects of the distribution are considered. |
