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Issue 12, 2009
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The long-chain dynamics in a model homopolymer blend under strong flow: small-angle neutron scattering and theory

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Abstract

We use small-angle neutron scattering (SANS) measurements to provide a detailed picture of the non-linear dynamics of the long chains in a model polystyrene blend. By a weighted subtraction of SANS measurements from two otherwise identical blends with different deuteration fractions, we isolate the single-chain form factor of the long-chain component of a model blend flowing through a 4 : 1 contraction–expansion flow. Complementary flow-birefringence also provides a measure of chain deformation on finer length-scales. In addition, higher flow Weissenberg numbers than in previous studies on monodisperse melts were achieved, leading to greater anisotropy in the measured single-chain structure factor. The short residence time inside the slit means that the chains are still oriented in the flow direction as they enter the contraction exit, leading to a rapid reversing flow. We compare these data to a simple generalisation of a non-linear tube model. Our model predictions are entirely ab initio, with all model parameters being determined from independent equilibrium measurements. The model shows very good agreement with the experimental data across the full range of length-scales for the contraction entrance and subsequent relaxation within the slit. However, there is conspicuous disagreement between theory and experiments at the contraction exit, in both the SANS and birefringence predictions, which we attribute to the reversing flow that occurs in this region.

Graphical abstract: The long-chain dynamics in a model homopolymer blend under strong flow: small-angle neutron scattering and theory

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Publication details

The article was received on 06 Oct 2008, accepted on 01 Dec 2008 and first published on 03 Feb 2009


Article type: Paper
DOI: 10.1039/B817440G
Citation: Soft Matter, 2009,5, 2383-2389
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    The long-chain dynamics in a model homopolymer blend under strong flow: small-angle neutron scattering and theory

    R. S. Graham, J. Bent, N. Clarke, L. R. Hutchings, R. W. Richards, T. Gough, D. M. Hoyle, O. G. Harlen, I. Grillo, D. Auhl and T. C. B. McLeish, Soft Matter, 2009, 5, 2383
    DOI: 10.1039/B817440G

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