Esmaeil Narimissa

A hierarchical multimode molecular stress function model for linear polymer melts in extensional flows

A novel hierarchical multimode molecular stress function (HMMSF) model for linear polymer melts is proposed, which implements the basic ideas of (i) hierarchical relaxation, (ii) dynamic dilution, and (iii) interchain tube pressure. The capability of this approach is demonstrated in modeling the extensional viscosity data of monodisperse, bidisperse, and polydisperse linear polymer melts. Predictions of the HMMSF model, which are solely based on the linear-viscoelastic relaxation modulus and a single free model parameter, the segmental equilibration time, are compared to elongational viscosity data of monodisperse polystyrene melts and solutions as well as to the elongational viscosity data of a bidisperse blend of two monodisperse polystyrenes, and good agreement between model and experimental data is observed. By using a simplified relation between the Rouse stretch-relaxation times and the relaxation times of the melts, the modeling is extended to the uniaxial, equibiaxial, and planar extensional viscosity data of a high-density polyethylene, the uniaxial and equibiaxial extensional viscosity data of a polydisperse polystyrene, the elongational viscosity data of three high-density polyethylenes, and a linear low-density polyethylene. For polydisperse melts, the modeling is again based exclusively on the linear-viscoelastic relaxation modulus with only one material parameter, the dilution modulus, which quantifies the onset of dynamic dilution.

A hierarchical multi-mode MSF model for long-chain branched polymer melts part I: elongational flow

A novel hierarchical multi-mode molecular stress function (HMMSF) model for long-chain branched (LCB) polymer melts is proposed, which implements the basic ideas of (i) the pom-pom model, (ii) hierarchal relaxation, (iii) dynamic dilution and (iv) interchain pressure. Here, the capability of this approach is demonstrated in modelling uniaxial extensional viscosity data of numerous broadly distributed long-chain branched polymer melts with only a single non-linear parameter, the dilution modulus.

A hierarchical multi-mode MSF model for long-chain branched polymer melts part II: multiaxial extensional flows

In part I, a novel hierarchical multi-mode molecular stress function (HMMSF) model for long-chain branched (LCB) polymer melts has been proposed, which implements the basic ideas of (i) the pom-pom model, (ii) hierarchal relaxation, (iii) dynamic dilution, and (iv) interchain pressure. Here, the capability of this approach is demonstrated in modelling the extensional viscosity data of a broadly distributed long-chain branched polymer melt in uniaxial, equibiaxial, and planar extensional deformations with only a single non-linear parameter, the dilution modulus, which quantifies the fraction of dynamically diluted chain segments.

A hierarchical multi-mode MSF model for long-chain branched polymer melts part III: shear flows

A novel hierarchical multi-mode molecular stress function (HMMSF) model for long-chain branched (LCB) polymer melts is proposed, which implements the basic ideas of (i) the pom-pom model, (ii) hierarchal relaxation, (iii) dynamic dilution, (iv) interchain pressure and (v) convective constraint release relaxation mechanism. Here, the capability of this approach is demonstrated in modelling the steady shear data of a broadly distributed long-chain branched polymer melt with only two non-linear parameters, a dilution modulus and a convective constraint release (CCR) parameter.

From melt to solution: Scaling relations for concentrated polystyrene solutions

The scaling relations established for the relaxation modulus of concentrated solutions of polystyrene (PS) in oligomeric styrene [Wagner, Rheol. Acta 53, 765–777 (2014); Wagner, J Non-Newtonian Fluid Mech. (2015)] are applied to the solutions of PS in diethyl phthalate (DEP) investigated by Bhattacharjee et al. [Macromolecules 35, 10131–10148 (2002)] and Acharya et al. [AIP Conf. Proc. 1027, 391–393 (2008)]. The scaling relies on the difference ΔTg between the glass-transition temperatures of the melt and the glass-transition temperatures of the solutions. ΔTg can be inferred from the reported zero-shear viscosities, and the Baumgaertel, Schausberger, and Winter (BSW) spectra of the solutions are obtained from the BSW spectrum of the reference melt with good accuracy. Predictions of the extended interchain pressure (EIP) model, which is based on the assumption that the relative interchain pressure in the melt and in the solutions is identical, are compared to the steady-state elongational viscosity data o...

On the origin of brittle fracture of entangled polymer solutions and melts

A novel criterion for brittle fracture of entangled polymer liquids is presented: Crack initiation follows from rupture of primary C–C bonds, when the strain energy of an entanglement segment reaches the energy of the covalent bond. Thermal fluctuations lead to a short-time concentration of the strain energy on one C–C bond of the entanglement segment, and the chain ruptures. This limits the maximum achievable stretch of entanglement segments to a critical stretch of fc≤6. Recent experimental data of Huang et al. [Phys. Rev. Lett. 117, 087801 (2016)]] and Huang and Hassager [Soft Matter 13, 3470–3474 (2017)] on fracture of solutions of nearly monodisperse polystyrenes dissolved in oligomeric styrene and of a well characterized polydisperse polystyrene melt, are in general agreement with this fracture criterion. For quantitative agreement, finite extensibility effects have to be considered.