Breakdown of Time–Temperature Equivalence in Startup Uniaxial Extension of Entangled Polymer Melts

Abstract

In rheological characterization of polymeric materials, the time−temperature superposition (TTS) principle allows us to acquire a wider spectrum of information on polymer dynamics. Although there are reports of the failure of TTS when both chain dynamics and local segmental dynamics are accessible at each of several temperatures, we have assumed that TTS would apply to describe the temperature dependence of transient responses of entangled melts to fast startup deformation. In this work we show that at the same effective rate (e.g., the same Rouse−Weissenberg number Wi R equal to the product of the Hencky rate and the Rouse time) of uniaxial extension the nonlinear responses of several polymer melts are each different at different temperatures, pointing to an evident breakdown of the TTS. Specifically, we will show that for the same Wi R well-entangled polymer melts rupture at relatively low temperatures, yet still 20−30 deg above the glass transition temperature T g , but undergo necking-like failure at higher temperatures. Thus, at the same Wi R , stress−strain curves are significantly different at different temperatures. Moreover, at the lower temperature, these polymer melts can reach an extreme level of extensibility at a critical Wi R , which is completely unattainable at higher temperatures. These TTS violating phenomena present a serious challenge to our existing theoretical understanding of nonlinear rheology of entangled polymeric liquids.

50th Anniversary Perspective: Polymers with Complex Architectures

“…Recently, following a similar synthetic procedure and using CDMSS and (CH 3 ) 2 SiCl 2 , Avgeropoulos’ group − synthesized well-defined H-type homopolymers of 3,4-PI (high 3,4 content, ∼55–60%) and through collaboration with Wang’s group rheological measurements were conducted. Interesting results were reported, leading to new theoretical models for the nonlinear dynamic behavior of long chain branched (LCB) polymers and their mixtures with the corresponding linear.…”

Rheology of Entangled Polymers Not Far above Glass Transition Temperature: Transient Elasticity and Intersegmental Viscous Stress

“…The SBR161 K is a random copolymer of styrene and butadiene (SBR), synthesized by Dr. Xiaorong Wang at Bridgestone Americas Center for Research and Technology and has been characterized before. 58 The PMMA125 K is poly(methyl methacrylate) from Plaskolite Inc. and with the item number CA-86. The H-shape 3, 4-polyisoprene (150 K backbone, 25K arm, 63% 3, 4 content) (H-PI) was synthesized at Ioannina, Greece.…”

“…Most of the applied rates fall into the shaded second crossover regime, as indicated in Figure 1a−c, that was usually not probed in previous studies of startup uniaxial extension of entangled polymer melts. 58,62 Consequently, the initial stress response well above the rubber elasticity curve has not been seen and studied in the literature, to the best of our knowledge. As the extension grows, the entanglement network starts to produce the familiar rubber-elastic contribution in addition to the viscous stress.…”

“…19,62 In other words, a significant number of entanglements would actually lock in, leading to non-Gaussian stretching of the entanglement network at high strains prior to a window-glass like rupture. 58,62 As an additional reference point, we have also carried out startup uniaxial extension at a much higher temperature of 150 °C for PS1M. At this temperature, the available extensional rate is insufficiently high for us to access the shaded regime in Figure 1a.…”

Dendrons and Dendritic Terpolymers: Synthesis, Characterization and Self-Assembly Comparison

“…Living polymerization techniques provide the opportunity to synthesize polymers with predictable molecular characteristics and monodisperse distributions. The aforementioned methodologies, due to the living nature of the propagating chain-ends, allow the synthesis of well-defined non-linear polymers, with precise molecular architectures such as star- [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ], H- [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], and dendritic-shaped materials [ 24 , 25 , 26 , 27 , 28 , 29 , 30 ], respectively. For the synthesis of dendritic polymers, anionic [ 31 , 32 , 33 , 34 ], click-chemistry [ 35 ] and organometal-catalyzed [ 36 ] techniques have already been employed and are reported in the literature.…”