Rheo-optical studies of the response of entangled polymer solutions to step changes in shear rate

Oberhauser, James P.; Pham, Kevin; Leal, L. Gary

doi:10.1122/1.1807845

Cited by 6 publications

(2 citation statements)

References 46 publications

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“…The experimentally determined value of C for the PBD comb was found to be C ¼ 2.2 Â 10 À9 m 2 /N, in good agreement with the literature [49,50]. In shear flow, the stress-optical rule was found to be valid for polymer melts and solutions but the accessible range of shear rates was generally relatively small and limited to low rates [19,[51][52][53][54][55]. Hence, we can only state with certainty that the rule is valid at low shear rates when the chains remain unstretched.…”

Section: Flow-birefringence and Stress-optical Rulesupporting

confidence: 74%

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

Snijkers¹,

Kirkwood²,

Vlassopoulos³

et al. 2016

Journal of Rheology

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We report upon the characterization of the steady-state shear stresses and first normal stress differences as a function of shear rate using mechanical rheometry (both with a standard cone and plate and with a cone partitioned plate) and optical rheometry (with a flow-birefringence setup) of an entangled solution of asymmetric exact combs. The combs are polybutadienes (1,4-addition) consisting of an H-skeleton with an additional off-center branch on the backbone. We chose to investigate a solution in order to obtain reliable nonlinear shear data in overlapping dynamic regions with the two different techniques. The transient measurements obtained by cone partitioned plate indicated the appearance of overshoots in both the shear stress and the first normal stress difference during start-up shear flow. Interestingly, the overshoots in the start-up normal stress difference started to occur only at rates above the inverse stretch time of the backbone, when the stretch time of the backbone was estimated in analogy with linear chains including the effects of dynamic dilution of the branches but neglecting the effects of branch point friction, in excellent agreement with the situation for linear polymers. Flow-birefringence measurements were performed in a Couette geometry, and the extracted steady-state shear and first normal stress differences were found to agree well with the mechanical data, but were limited to relatively low rates below the inverse stretch time of the backbone. Finally, the steady-state properties were found to be in good agreement with model predictions based on a nonlinear multimode tube model developed for linear polymers when the branches are treated as solvent. V C 2016 The Society of Rheology.

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Section: Flow-birefringence and Stress-optical Rulesupporting

confidence: 74%

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

Snijkers¹,

Kirkwood²,

Vlassopoulos³

et al. 2016

Journal of Rheology

Self Cite

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show abstract

“…Experiments at other shear rates confirm that the overshoot occurs at a fixed strain and emphasize the hydrodynamic origin of the response. In the same vein, flow reversal experiments are commonly used to probe the structure of textured materials like liquid crystal polymers − and rigid-rod suspensions as well as immiscible polymer blends − and entangled homopolymers. − In these presheared experiments, the sample was melted and then immediately sheared at a rate of 0.1 s -1 at 180 °C until the viscosity reached steady state (5 min). The sample was then annealed for various times and temperatures before the same 0.1 s -1 shear rate was imposed in the reverse direction.…”

Section: Methodsmentioning

confidence: 99%

Soft Glassy Dynamics in Polypropylene−Clay Nanocomposites

Treece

Oberhauser

2007

Macromolecules

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Linear and nonlinear viscoelastic measurements were utilized to probe transient morphological changes in a melt-blended polypropylene-clay nanocomposite containing 3 wt % organically modified montmorillonite clay, 10 wt % maleic anhydride functionalized polypropylene (1% maleic anhydride content), and 87 wt % polypropylene homopolymer. Steady shear rate sweeps show that the viscosity decreases monotonically with shear rate, characteristic of a mechanically percolated material with a yield stress. Subsequent sweeps following annealing of up to 2 h show that the viscosity at low shear rates remains substantially lower than the initial sweep, indicative of slow or arrested organoclay disorientation. In startup of shear flow, as-processed and presheared nanocomposite samples both exhibit increasing viscosity overshoots with annealing time for up to 6 h, although the overshoots for the presheared samples remain uniformly smaller than those of the as-processed material. Similarly, small-amplitude oscillatory shear experiments on as-processed and presheared samples also reveal that the storage modulus and complex viscosity increase logarithmically with time, while the loss tangent declines steadily. Both sets of data point to increasingly solidlike rheology over time, a phenomenon that is discussed in the context of soft glassy dynamics.

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A full-chain stochastic tube model for entangled melts and solutions of linear polymers

Denn

Schieber

2006

Journal of Rheology

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Rheo-optical studies of the response of entangled polymer solutions to step changes in shear rate

Cited by 6 publications

References 46 publications

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

Soft Glassy Dynamics in Polypropylene−Clay Nanocomposites

A full-chain stochastic tube model for entangled melts and solutions of linear polymers

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