Concept of Stretch/Orientation-Induced Friction Reduction Tested with a Simple Molecular Constitutive Equation

Abstract

Under elongational flow at strain rates higher than the Rouse relaxation frequency, entangled polymer melts exhibit thinning of their elongational viscosity whereas equally entangled solutions show thickening. Yaoita et al. [Yaoita et al., Macromolecules 2012, 45, 2773 related this difference between the melts and solutions to reduction of segmental friction on enhancement of the stretch/orientation averaged for the components therein (that includes the solvent for the case of solutions). They analyzed the stress relaxation data after cessation of elongational flow to propose an empirical equation describing this friction reduction as a function of the stretch/orientation factor. Multi-chain slip-link (PCN) simulations considering this friction reduction described the thinning of melts and the thickening of solutions consistently and semi-quantitatively. This study further tests the molecular concept of the stretch/orientation-induced friction reduction with the aid of a simple molecular constitutive equation, a toy version of the Mead-Larson-Doi model [Mead et al., Macromolecules 1998, 31, 7895] (MLD toy model) being modified to incorporate this empirical equation of the friction reduction. The modified toy model mimicked the behavior of melts and solutions consistently. This consistency vanished when the friction reduction in the model was artificially switched off, even though the finite extensible nonlinear elasticity was still taken into account. These results lend further support to the molecular concept of the stretch/orientation-induced friction reduction.

Primitive chain network simulations for elongational viscosity of bidisperse polystyrene melts

“…The primitive chain network simulations with the SORF implementation mentioned above has attained semi-quantitative agreement with experiments for entangled polymer solutions and melts of linear polymers [15,17] and a pom-pom branch polymer [16]. It is noteworthy that the same SORF relationship has been examined via the tube model as well [26].…”

Analysis of Elongational Viscosity of Entangled Poly (Propylene Carbonate) Melts by Primitive Chain Network Simulations

“…including bidisperse [17] and branch systems [18,19] to demonstrate the consistency of the friction change for different systems. Similar studies have been conducted for molecular constitutive equations [1,[20][21][22][23][24].…”

Nonlinear Elongational Rheology of Unentangled Polystyrene and Poly(p-tert-butylstyrene) Melts

“…In contrast, ICP formulated in the molecular stress function model by Wagner and co-workers may contribute to the elongational behavior significantly, but the importance of ICP was not found in recent analysis by Desai and Larson . Interestingly, the tube model phenomenologically modified for the ζ reduction can mimic the elongational data of entangled melts, as shown by Desai and Larson and by Masubuchi and co-workers . Nevertheless, in this modified model, the ζ reduction is strongly coupled with the nonlinearities of entanglement relaxation assumed in the model, so that the details of the ζ reduction have not been fully elucidated.…”

“…30 Interestingly, the tube model phenomenologically modified for the ζ reduction can mimic the elongational data of entangled melts, as shown by Desai and Larson 30 and by Masubuchi and co-workers. 31 Nevertheless, in this modified model, the ζ reduction is strongly coupled with the nonlinearities of entanglement relaxation assumed in the model, so that the details of the ζ reduction have not been fully elucidated.…”