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An extended interchain tube pressure model for polymer melts and concentrated solutions is presented, based on the idea that the pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic (M. Doi and S. F. Edwards, The Theory of Polymer Dynamics, Oxford University Press, New York, 1986). In a tube model with variable tube diameter, chain stretch and tube diameter reduction are related, and at deformation rates larger than the inverse Rouse time τR, the chain is stretched and its confining tube becomes increasingly anisotropic. Tube diameter reduction leads to an interchain pressure in the lateral direction of the tube, which is proportional to the 3rd power of stretch (G. Marrucci and G. Ianniruberto. Macromolecules 37, 3934-3942, 2004). In the extended interchain tube pressure (EIP) model, it is assumed that chain stretch is balanced by interchain tube pressure in the lateral direction, and by a spring force in the longitudinal direction of the tube, which is linear in stretch. The scaling relations established for the relaxation modulus of concentrated solutions of polystyrene in oligomeric styrene (M. H. Wagner, Rheol. Acta 53, 765-777, 2014, M. H. Wagner, J. Non-Newtonian Fluid Mech. http://dx.doi.org/10.1016/j.jnnfm.2014.09.017, 2014) are applied to the solutions of polystyrene (PS) in diethyl phthalate (DEP) investigated by Bhattacharjee et al. (P. K. Bhattacharjee et al., Macromolecules 35, 10131-10148, 2002) and Acharya et al. (M. V. Acharya et al. AIP Conference Proceedings 1027, 391-393, 2008). The scaling relies on the difference ΔTg between the glasstransition temperatures of the melt and the glass-transition temperatures of the solutions. ΔTg can be inferred from the reported zero-shear viscosities, and the BSW spectra of the solutions are obtained from the BSW spectrum of the reference melt with good accuracy. Predictions of the EIP model are compared to the steady-state elongational viscosity data of PS/DEP solutions. Except for a possible influence of solvent quality, linear and nonlinear viscoelasticity of entangled polystyrene solutions can thus be obtained from the linear-viscoelastic characteristics of a reference polymer melt and the shift of the glass transition temperature between melt and solution. [ABSTRACT FROM AUTHOR]

Precise evaluation and notional prediction of extensional rheological behaviour of polymeric melts and solutions are of significant importance in polymer industry. This is evident in the well documentation of the dominance of elongational deformation of polymeric systems in processes such as melt spinning, blow moulding, biaxial stretching of extruded sheets, etc. The relevant commercial extensional rheometers thus far discussed in the literature are RME and SER. This research, for the first time, compares the extensional viscosity measurements of low density polyethylene at 140, 150, and 170 °C through RME and SER devices. Despite the observed similarities found in this comparative investigation, the main difference was laid in maximum Hencky strain, strain hardening viscosity, and the variation of those rheological properties with testing temperature of the samples. [ABSTRACT FROM AUTHOR]

MAOS is shown to be a powerful tool to investigate the inception of nonlinear viscoelasticity of polymer melts. A constitutive analysis based on a general single integral constitutive equation, which includes the Doi-Edwards model without (DE) and with independent alignment assumption (DE IA) as well as the molecular stress function (MSF) model, confirms two important scaling relations found experimentally by Hyun and Wilhelm: (1) The relative intensity of the 3rd harmonic compared to the 1st harmonic scales with the square of the strain amplitude according. Consequently, a new nonlinear coefficient, the so-called intrinsic nonlinearity was introduced. (2) In the terminal relaxation regime, the intrinsic nonlinearity scales with the square of the angular frequency, and was found to be a very sensitive measure regarding molecular topology by identifying and separating relaxation processes in model branched polymers. We show that the nonlinear viscoelastic moduli can be expressed as sums of their linear-viscolelastic counterparts at angular frequencies of ω, 2ω, and 3ω. The absolute value of the intrinsic nonlinearity depends on the difference (α-β) between the 3rd order orientational effect (parameter α) according to the DE or DE IA model and the 2nd order isotropic stretching effect (parameter β) according to the MSF model. The measured apparent values of the intrinsic nonlinearity measured in parallel-plate geometry are rescaled in order to take the non-uniform shear deformation into account, and are compared to constitutive models. While both the DE and DE IA model fail to describe the experimental data, the data of linear and comb-like PS melts are quantitatively described by the MSF model. However, the model predicts a plateau at the level of the maximum of the experimental data, while for comb polymers with entangled branches, a minimum in the intrinsic nonlinearity is observed, followed by a second increase of the intrinsic nonlinearity at higher frequencies, which correspond to the terminal relaxation times of the branches. Surprisingly, this can be modelled quantitatively if only the terminal relaxation modes of the backbone and the branches are assumed to be deforming non-affinely and to respond to the nonlinearity. [ABSTRACT FROM AUTHOR]