Abstract
The apparent viscosity of dilute polymer solutions in non-inertial flows through channels consisting of successive short tubes or slits separated by expansions displays a marked divergence from shear-thinning power-law behaviour beyond a critical shear rate calculated for constricted sections. The product of this critical shear rate by the Rouse relaxation time was found to be nearly constant for various coil polymers, solvent viscosities and polymer concentrations, independently of the exact geometric shape of the channels. When the critical shear rate is reached, the maximum stretch rate in the converging sections is greater than the inverse of the Rouse relaxation time. An elongation of macromolecules is thus expected and the dilatant behaviour can be attributed to the increased viscous dissipation due to the elongated state of macromolecules in the converging parts of flow.
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