A variety of rheological measurements including oscillatory shear and steady shear in both controlled rate and controlled stress modes has been carried out to unravel the universal flow characteristics of different entangled polymers under the fast flow condition defined as applied shear rates reaching beyond the overall chain relaxation rate and/or applied stresses as high or higher than the dynamic plateau modulus. Flow birefringence and particle imaging velocimetry have been applied to detect any spatial variation of the shear rate across the sample under both controlled rate and controlled stress conditions. Our findings challenge the current theoretical knowledge (a) of the fast flow behavior of entangled polymers. (a) J. Bent et al, Science 301, 1691 (2003); R. Graham, A. Likhtman, T. McLeish and S. Milner, J. Rheol. 47, 1171 (2003).
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