Stress Relaxation of Comb Polymers with Short Branches

Kirkwood, Keith M.; Leal, L. Gary; Vlassopoulos, Dimitris; Driva, Paraskevi; Hadjichristidis, Nikos

doi:10.1021/ma900950s

Cited by 68 publications

(96 citation statements)

References 78 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].…”

Section: Flow-birefringence and Stress-optical Rulesupporting

confidence: 86%

“…Subsequently, we discuss and compare the steadystate shear stress and first normal stress difference as a function of shear rate, as obtained mechanically and optically. Finally, we show that both nonlinear stresses can be quantitatively described with a tube model developed for linear polymers when treating the branches as dynamic solvent, as already qualitatively observed in [33,34].…”

Section: Introductionsupporting

confidence: 70%

“…The value of A is fixed at 2.4045 during calibration. Details of the calibration and alignment of the optical train can be found in [49]. The polarization of the laser beam is now modulated at x=2p (42.09 kHz) and passes through a quarter wave retarder oriented at 0 .…”

Section: Flow-birefringence and Stress-optical Rulementioning

confidence: 99%

“…The birefringence can be calculated from the retardance d using the standard relationship Dn 0 ¼ kd=2ph with k ¼ 632.8 nm being the wavelength of the laser light and h being the height of the Couette shear cell. Without further details, for our setup, the unknown orientation angle and retardance of the polymer sample, v and d, respectively, can be found from [49] …”

Section: Flow-birefringence and Stress-optical Rulementioning

confidence: 99%

“…For the nonlinear shear flow data instead, we attempted to describe the steady-state shear viscosity and first normal stress difference with a model for linear polymers which is justified based on an earlier work where we found that combs with relatively short branches behave essentially like linear polymers in nonlinear shear flow with some small quantitative differences [33,34]. Strong qualitative as well as quantitative differences in the nonlinear shear flow behavior only became apparent when the branches were "long" and comprise more than about 70% of the total molecular structure [63].…”

Section: E Tube-based Modelingmentioning

confidence: 99%

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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: 86%

Section: Introductionsupporting

confidence: 70%

Section: Flow-birefringence and Stress-optical Rulementioning

confidence: 99%

Section: Flow-birefringence and Stress-optical Rulementioning

confidence: 99%

Section: E Tube-based Modelingmentioning

confidence: 99%

See 3 more Smart Citations

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

Snijkers¹,

Kirkwood²,

Vlassopoulos³

et al. 2016

Journal of Rheology

View full text Add to dashboard Cite

show abstract

Rheological Measurements

2013

Encyclopedia of Polymer Science and Technology

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Rheology is the science to study the flow and deformation of matter. It becomes an important field in material science and engineering, food, biotechnology, and so on. The objects in rheological study are not the ideal solid and ideal fluid, which can be described by the Hookean elastic model and the Newtonian viscous model, respectively. Instead, the rheological study often focuses on materials that can exhibit viscous, elastic, and plastic behavior under different flow conditions. They are often termed as complex fluids or soft matter, which include polymers, gels, suspensions, emulsions, biofluids, foods, inks (1). In contrast to hydrodynamics, which often accounts for the complex flow behavior of simple fluids, simple geometry is utilized in rheological measurements to understand the rather complicated relationship between the mechanical input and output of complex fluids. The real flow fields encountered in many applications (such as polymer extrusion, injection molding, blow molding, fiber spinning, inkjet printing, coating) are rather complicated (2). It becomes a problem whether the rheological measurements that performed under simple flow fields are useful in understanding the complicated flow behaviors of complex fluids. Fortunately, it has been proved in many examples that the properties determined from simple rheological measurements are sufficient to quantify the material parameters in various constitutive equations, which have been used widely and successfully to simulate the flow behaviors in polymer processing (3-11). The most frequently used simple flow fields are simple shear flow and simple extensional flow.The simplest geometry that defines the simple shear is two infinite parallel plates separated by a distance h. The liquid is set between two plates with one plate moving parallel to the other (Fig. 1). In reality, when the length L and the width B are much larger than the gap h, the flow in the center regime resembles the flow between two infinite plates. It means that the edge effects are ignored in most experimental shear geometries. In rheological measurements, the flow between two plates should be laminar. Moreover, it is usually assumed that the velocity across the gap satisfies a linear profile. As shown in Fig. 1, if the bottom plate is fixed and the upper plate moves horizontally with the velocity V, the fluid velocity varies linearly from 0 at the bottom plate to V at the upper plate if the no-slip boundary condition is satisfied. The linear velocity profile generates a constant velocity gradient, which is known as the shear rate. Then, the flow field between two parallel plates is homogeneous in the shear rate. The homogeneous assumption is nontrivial in the rheological tests since the actual velocity

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Unraveling the cause for the unusual processing behavior of commercial partially bio‐based poly(butylene succinates) and their stabilization

Hallstein

Gomoll

Lieske

et al. 2021

J of Applied Polymer Sci

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The commercially available partially bio‐based poly(butylene succinate) (PBS) and poly(butylene succinate‐co‐adipate) (PBSA) are subjected to prolonged and multiple extrusion cycles to investigate their thermal behavior. Empirically, both PBS and PBSA form branches at 190°C, with PBS possessing a higher tendency for branching than PBSA as studied by rheology and size exclusion chromatography (SEC). In each case, the branching is favored by fumaric acid moieties, making both PBS and PBSA susceptible to accelerated thermal oxidation. Indeed, the NMR signal attributed to fumaric acid disappears upon thermal processing of PBS and PBSA. Presumably, the bio‐based succinic acid used contains minor quantities of fumaric acid, yet still sufficient to cause this surprising processing behavior. The branching of both polymers is suppressed by stabilizers such as phenolic antioxidants, as proven by rheology and SEC. This is complemented by nuclear magnetic resonance (NMR), revealing that the fumaric acid signal is still well‐resolved in the stabilized processed samples.

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Stress Relaxation of Comb Polymers with Short Branches

Cited by 68 publications

References 78 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

Rheological Measurements

Unraveling the cause for the unusual processing behavior of commercial partially bio‐based poly(butylene succinates) and their stabilization

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