화학공학소재연구정보센터
Macromolecules, Vol.47, No.19, 6768-6775, 2014
Test of Orientation/Stretch-Induced Reduction of Friction via Primitive Chain Network Simulations for Polystyrene, Polyisoprene, and Poly(n-butyl acrylate)
Entanglement dynamics of polymers under fast elongation has not been fully understood. Namely, the steady-state uniaxial elongational viscosity of entangled polystyrene (PS) solutions increases with an increase of strain rate above the reciprocal Rouse time, whereas the viscosity of PS melts monotonically decreases even at such high rates. This qualitative difference between solution and melt has been hypothesized to result from the orientation/stretch-induced reduction of friction (SORE). This study examines universality of the mechanism of SORE for narrowly distributed PS, polyisoprene (PI), and poly(n-butyl acrylate) (PnBA). For this purpose, SORE was incorporated in the multichain slip-link simulation through an empirical relationship between the magnitude of friction reduction and the stretch/orientation order parameter for PS [reported in Macromolecules 2012, 45, 2773-2782]. This empirical SORE relationship adopted a mean-field view for contacts between polymer backbone and solvent, and the simulation having this mean-field feature was confirmed to reproduce satisfactorily the transient and steady elongational viscosity data for PS melts and solutions. Assuming that the magnitude of SORE is insensitive to the chemical structure of polymers, we further made the simulation with the same SORE relationship for PI and PnBA. For PI, the simulation reasonably described the viscosity data of a melt and solutions. However, for PnBA melt, the data were well described by the simulation but without SORF. This result suggests that the magnitude of SORE is not universal but changes with the chemical structure of polymers. Specifically, for PnBA, the flexible side chains always surround the PnBA backbone and may behave as a solvent to screen the direct interaction between the backbone segments even in melt. For this case, the mean-field type SORE relationship obviously fails. Nevertheless, a non-mean-field type SORE could result in negligible friction reduction even under fast elongation, thereby allowing the simulation without SORE to describe thet data for PnBA.