New Experiments for Improved Theoretical Description of Nonlinear Rheology of Entangled Polymers

Abstract

The present work discusses four types of new experiments that can improve the current theoretical description of nonlinear rheology of entangled polymers. First, a slowly imposed strain is found to result in nonmonotonic evolution of the state of chain entanglement during quiescent relaxation, consistent with the idea of chain disentanglement after step shear. Second, the stress relaxation upon a sizable step strain is found to be identical to that for small step strain, consistent with a molecular scenario that a strained entangled melt has an entropic barrier to resist chain retraction. Third, the ability of a step-strained polymer to undergo elastic recovery is found to be the same up to strain amplitude of unity, and a sample sheared for a period much longer than the Rouse time is shown to still undergo nearly full elastic recovery. Fourth, an entangled melt, stretched at a rate significantly lower than the Rouse relaxation rate, undergoes full elastic recovery until the point of tensile force maximum. We have discussed an alternative conceptual framework to describe these nonlinear responses of entangled polymers despite the possibility that the tube model might be further remedied to characterize the new rheometric measurements presented in this work.

A force-level theory of the rheology of entangled rod and chain polymer liquids. I. Tube deformation, microscopic yielding, and the nonlinear elastic limit

“…al. [17][18][19]22]. However, our present analysis does not address the issue of the time scale at which chain retraction occurs.…”

“…Open questions include the following [5,[15][16][17][18][19][20][21][22][23][24][25]. Do chains that have been stretched by deformation freely retract in a Rouse-like manner and on Rouse-like time scales?…”

Rheological characterizations of wormlike micellar solutions containing cationic surfactant and anionic hydrotropic salt

“…The "yield like" behavior exhibited in these systems is due to the entangled/disentangled micelle chains Wang (2004, 2006)], especially under periodic flow at large amplitudes. The imbalance of two forces, the elastic retraction force from shear, and the extension force from the entanglement points can induce disentangled chains, accompanied by the homogeneous elastic deformation within wormlike micellar networks [Wang et al (2013)]. In our case (s r > 1=x), with increasing strain c, the micellar networks kept on yielding and the stress was more likely to accumulate and relax in the entangled network, accompanied by the viscous dissipation during the deformation period.…”

Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

“…10,39,50,51 This failure lies in its poor treatment of chain disentanglement during large mechanical deformations that lead to nonlinear responses. 52 The mounting experimental evidence of complex entanglement dynamics and stress nonlinearities not captured by the DE model, 39,51 has led to the emergence of tube model extensions such as con-vective constraint release (CCR), cohesive yielding, stress-induced tube dilation, and anharmonic tube potential softening, all of which dynamically alter the density and propensity of entanglements surrounding each filament. 39,51,[53][54][55] CCR models postulate that the imposed shear forces surrounding entanglements to disentangle at rate controlled by the shear rate, allowing each filament to relax over a much faster timescale than reptation.…”