Shear-induced concentration fluctuations and form factor changes in polymer solution in the good-solvent regime
Laboratoire de spectrométrie physique, CERMO, UJF - CNRS UMR 5588, F-38402 , Saint Martin d’Héres, France
2 Institut Laue et Langevin, Ave. des martyrs, F-38049, Grenoble, France
3 Laboratoire Léon Brillouin, CEA Saclay, F-91191, Gif-sur-Yvette, France
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Small-Angle Scattering from sheared semidilute polymer solution is reported in the good-solvent regime, at variance with former light and neutron measurements in the regime. First, concentration fluctuations are observed: the scattering increases noticeably along the flow at low q, but at variance with former results for the theta-solvent regime, no demixing is observed at higher shear. Here, instead, the effects follow a time-temperature superposition and saturate above a Weissenberg number around 5, like the stress which is known to present a plateau for these systems. Using the Zero Average Contrast technique, we have also measured the form factor, which displays the same saturation effect reaching a deformation ratio of the order of 2. These results agree with the Convective Constraint Release models (CCR) elaborated in order to predict the stress effects in the non-Newtonian regime (Marrucci-Ianniruberto) and their extension predicting also the scattering (Likhtman-Milner-McLeish).
© EDP Sciences, Società Italiana di Fisica, and Springer-Verlag, 2004