화학공학소재연구정보센터
Rheologica Acta, Vol.60, No.4, 163-174, 2021
Elongational viscosity scaling of polymer melts with different chemical constituents
Morelly et al. (Macromolecules 52:915-922, 2019) reported transient and steady-state elongational viscosity data of monodisperse linear polymer melts obtained by filament-stretching rheometry with locally controlled strain and strain rate and found different power law scaling of the elongational viscosities of polystyrene, poly(tert-butylstyrene) and poly(methyl-methacrylate). Very good agreement is achieved between data and predictions of the extended interchain pressure (EIP) model (Narimissa et al. J. Rheol. 64, 95-110 (2020)), based solely on linear viscoelastic characterization and the Rouse time tau(R) of the melts. The analysis reveals that both the normalized elongational viscosity and the normalized elongational stress are dependent on the number of entanglements (Z) and the ratio of entanglement molar mass M-em to critical molar mass M-cm of the melts in the linear viscoelastic regime through eta(0)(E)/(G(N) tau(R)) proportional to (M-em/M-cm) (2.4)Z(1.4) and sigma(0)(E)/G(N) proportional to (M-em/M-cm) (2.4)Z(1.4)Wi, while in the limit of fast elongational flow with high Weissenberg number Wi = tau(R)(epsilon)over dot, both viscosity and stress become independent of Z and M-em/M-cm, and approach a scaling which depends only on Wi, i.e. eta(E)/(G(N)tau(R)) proportional to Wi(-1/2) and sigma(E)/G(N) proportional to Wi(1/2). When expressed by an effective power law, the broad transition from the linear viscoelastic to the high Wi regime leads to chemistry-dependent scaling at intermediate Wi depending on the number of entanglements and the ratio between entanglement molar mass and critical molar mass.