Shear thinning of unentangled flexible polymer liquids

Colby, Ralph H.; Boris, David C.; Krause, Wendy E.; Dou, Shichen

doi:10.1007/s00397-006-0142-y

Cited by 89 publications

(108 citation statements)

References 38 publications

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“…4,5 In principle, the stretching of a neutral chain under an elongational flow and the extension of a polyelectrolyte chain under the electrostatic repulsion have a similar physical nature, but not identical. Namely, a neutral chain can be stretched as a string of blobs under an elongational flow.…”

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confidence: 99%

How Much Force Is Needed To Stretch a Coiled Chain in Solution?

Jin

et al. 2009

Macromolecules

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In the 1970s, de Gennes and Pincus 1,2 used the Rouse model 3 to show that linear polymer chains in a good solvent could undergo a first-order coil-to-stretch transition to pass through a pore much smaller than its coiled size under an elongation flow field with a sufficient hydrodynamic force, independent of both the chain length and the pore size. Namely, a coiled polymer chain can pass through a small pore as long as the flow rate (q) is higher than a threshold [q c = k B T/(3πη)], where k B , T, and η is the Boltzmann constant, the absolutely temperature, and the solvent viscosity, respectively.On the other hand, it has been suggested that the electrostatic blob model for a polyelectrolytes chain would also be applicable for the coil-to-stretch transition of a neutral chain in an ultrafiltration experiment. 4,5 In principle, the stretching of a neutral chain under an elongational flow and the extension of a polyelectrolyte chain under the electrostatic repulsion have a similar physical nature, but not identical. Namely, a neutral chain can be stretched as a string of blobs under an elongational flow. The blob size decreases as the shear rate increases. Finally, each blob can be fully stretched with a sufficiently strong shear force.It is not difficult to realize that the passing through a small pore occurs only when the blob size (ξ b ) of a stretched chain in a flow filed is smaller than the pore size (D). Therefore, the critical flow rate is associated with the relative size of the blob to the pore. Whether a coiled chain can pass through a small pore is related to its local deformability, i.e., the entering of the first blob into the pore, at which the entropic confinement force (k B T/D) is overcame by the hydrodynamic force (3πηq c /D), where it has assumed that each blob is a nondraining ball with a diameter identical to the pore size (D). 1,2 Note that here only the short-range interaction is relevant. In principle, one can reversibly use q c to characterize the local deformability. To our knowledge, the predicted chain-length and pore-size independence of q c has not been confirmed in experiments because such a first-order coil-tostretch transition has not been observed for a long time. Recently, we have observed such a discontinuous first-order transition by ultrafiltrating linear polystyrene chains through specially constructed small pores (20 nm). 6

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confidence: 99%

How Much Force Is Needed To Stretch a Coiled Chain in Solution?

Jin

et al. 2009

Macromolecules

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“…The semi-dilute polymer solutions showed a pronounced shear thinning behavior, as determined by rheometer measurements (Colby et al 2006) (Fig. 2a).…”

Section: Resultsmentioning

confidence: 72%

“…Consequently, the flow profile is determined by the relaxation of the polymers at high shear rates _ c [ 1=s rheo . In this regime, polymers that are exposed to higher shear rates reach their steady state faster, since with higher shear rates only modes of the polymers with short relaxation times can relax (Colby et al 2006). Consequently, the steady state of the polymer configuration is further away from the initially stretched state for polymers exposed to low shear rates than for polymers exposed to higher shear rates.…”

Section: Resultsmentioning

confidence: 99%

“…Above a certain extensional rate, which is mandatory to start the extension of the polymers from their equilibrium conformation, this outcome is independent of the flow rate (Perkins 1997;Smith 1998;Larson et al 1999). The relaxation of the initially stretched polymers in shear flow after the contraction causes an increase in their hydrodynamic diameter and consequently an increase in the dissipation of energy (Colby et al 2006). Therefore, the local viscosities along the flow direction increase until the polymers reach their steady-state conformation.…”

Section: Resultsmentioning

confidence: 99%

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Transient flow behavior of complex fluids in microfluidic channels

Kleβinger

Wunderlich

Bausch

2013

Microfluid Nanofluid

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The ongoing development of microfluidic devices involves the use of highly complex fluids, even of multiphase systems. Despite the great achievements in the development of numerous applications, there is still a lack in the complete understanding of the underlying physics of the observed macroscopic effects. One prominent example is the flow through benchmark contractions where microand even macroscopic explanations of some of the occurring flow patterns are still missing. Here, we study the development of the flow profiles of shear thinning semidilute polymer solutions in microfluidic planar abrupt contraction geometries. Flow profiles along the narrow channel part are obtained by l-PIV measurements, whereby the pressure drop along the microfluidic channel as well as the local transient viscosities downstream to the orifice are computed. A relaxation process of the flow profiles from an initially parabolic shape to the flattened steady-state flow profile is observed and traced back to the polymer relaxation.

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“…This behavior can be rationalized if we consider that a specific kind of motion will only be affected if the frequency of an external stimuli ͑here shear͒ becomes comparable or larger than the characteristic frequency of this motion, i.e., here if ␥ ‫ء‬ Ն 1, where represents the characteristic time of the studied process at rest. 52 For the slower process, this condition holds for all the applied strain rates, while for the faster process only for ␥ ‫ء‬ Ϸ 0.3 and larger. The apparent similarity of the distributions describing the fast process ͓in terms of the location, the width, and the amplitude of the fast peak, Figs.…”

Section: -7mentioning

confidence: 93%

Shear-induced effects in hyperbranched-linear polyelectrolyte complexes

Dalakoglou

Karatasos

Lyulin

et al. 2008

The Journal of Chemical Physics

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Static and dynamic properties of complexes formed by hyperbranched polymers with linear polyelectrolytes are studied under the influence of steady shear flow by means of Brownian dynamics simulations. Models of peripherally charged hyperbranched molecules bearing two extreme topological structures and different molecular weights complexed with linear neutralizing chains are subjected to a range of shear rates starting from a low-shear regime toward the complex-breaking point. Examination of the stability limit, shape and mass distribution parameters, and dynamics in different lengths and timescales is performed as a function of the applied shear. The results described illustrate features of the generic behavior that should be expected from such systems under conditions of steady shear flow.

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Shear thinning of unentangled flexible polymer liquids

Cited by 89 publications

References 38 publications

How Much Force Is Needed To Stretch a Coiled Chain in Solution?

How Much Force Is Needed To Stretch a Coiled Chain in Solution?

Transient flow behavior of complex fluids in microfluidic channels

Shear-induced effects in hyperbranched-linear polyelectrolyte complexes

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