Flow-Induced Nematic Interaction and Friction Reduction Successfully Describe PS Melt and Solution Data in Extension Startup and Relaxation

The uniaxial extensional-flow data of Huang and co-workers [ACS Macro Lett. 2013, 2, 741; J. Rheol. 2016, 60, 465] on several polystyrene systems, both melts and solutions, are here successfully compared with the predictions of a recent model [Ianniruberto, Macromolecules 2015, 48, 6306] that accounts for flow-induced friction-coefficient reduction. The model is here effectively simplified without loss of accuracy. Comparison with the solution data of Huang et al. [ACS Macro Lett. 2013, 2, 741], only differing for the size of the oligomeric solvent (from nearly one Kuhn length up to a few ones), reveals that friction reduction must include oligomer-size-dependent orientational coupling between the oligomeric solvent and the polymer molecules, such interactions vanishing for the smallest oligomer. The rheological “measure” of this nematic-like interaction as a function of the oligomer size (for small oligomers) is the novel result of the present paper, together with a further confirmation of the importance...