Nonlinear rheometry of entangled polymeric rings and ring-linear blends

Abstract

We present a comprehensive experimental rheological dataset for purified entangled ring polystyrenes and their blends with linear chains in nonlinear shear and elongation. In particular, data for shear stress growth coefficient, steady-state shear viscosity, and first and second normal stress differences are obtained and discussed as functions of shear rate as well as molecular parameters (molar mass, blend composition and decreasing molar mass of linear component in blend). Over the extended parameter range investigated, rings do not exhibit clear transient undershoot in shear, in contrast to their linear counterparts and ring-linear blends. For the latter, the size of the undershoot and respective strain appear to increase with shear rate. Universal scaling of strain at overshoot and fractional overshoot (ratio of maximum to steady-state shear stress growth coefficient) indicates subtle differences in the shear-rate dependence between rings and linear polymers or their blends.

Rheological Properties of Ring Polymers and Their Derivatives

“…They discovered that under start-up shear flow the ring PS exhibits weaker shear thinning with less stress overshoot than the corresponding linear PS. Parisi et al 21,22) recently reported the same trend even for a ring PS with higher M (= 185 kg/mol) (Fig. 2).…”

“…Regarding the NLVE of ring/linear polymer blends, Parisi et al 22) examined the nonlinear shear rheology of sym-…”

Some open challenges in polymer physics*

“…Thus, there seem to be two possible regimes of behavior for the viscosity considering the most recent results on polystyrene rings. Either they follow the Rouse-like behavior as suggested by Doi et al's data [131,132,144] or there is a rapid upturn due to entanglement that would be suggested by the data from Kapnistos et al, [129] Pasquino et al, [130] Yan et al, [146] and Parisi et al [145] Because these samples have been made by a ring closure procedure in dilute solution, getting substantially larger pure ring samples seems problematic and newer methods for large ring synthesis are needed. [147] We now return to the problem of the steady state recoverable compliance of the polymer rings and look at the materials that have been fractionated by the LCCC method.…”

“…Similarly, a rough estimate performed on the published [ 130 ] stress relaxation curves for polyisoprene and for the Kapnistos polystyrene rings seem to have too strong a molecular weight dependence, viz., for the polystyrene rings while for the polyisoprene rings it seems to vary approximately as , both of which are much stronger dependences than expected from theory [ 143 ] of . Though the above leads to some important questions, the field has gone beyond the results of Kapnistos, et al [ 129 ] and the compilation and new data from Pasquino et al [ 130 ] was also of interest, but newer data from Doi et al [ 131,132,144 ] using LCCC fractionated rings and of Parisi et al [ 145 ] using both LCCC and conventionally fractionated rings suggest that the Kapnistos et al [ 129 ] data may have had a higher linear chain content than originally thought. In Figure 32, we show the polystyrene results from the McKenna et al data, that from Roovers prior to LCCC treatment, the Kapnistos et al data on LCCC treated PS and the Pasquino et al data that included the Kapnistos results as well as results for a sample with a molecular weight of 240,000 g/mol.…”

“…We remark that the Parisi et al [ 145 ] data for Doi et al [ 131 ] did not note that the 2015 data for the 244,000 g/mol sample had been corrected by further refinement of the samples and extrapolation to zero concentration of linear chains. [ 132 , 144 ] Also, Parisi et al [ 145 ] reported a new value for the Kapnistos et al [ 129 ] 198,000 g/mol sample…”