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

Graham, Richard S.; Bent, Julian; Clarke, Nigel; Hutchings, Lian R.; Richards, Randal W.; Gough, Tim; Hoyle, David M.; Harlen, Oliver G.; Grillo, Isabelle; Auhl, Dietmar; McLeish, Tom C.B.

Authors

Richard S. Graham

Julian Bent

Nigel Clarke

Randal W. Richards

Tim Gough

David M. Hoyle

Oliver G. Harlen

Isabelle Grillo

Dietmar Auhl

Tom C.B. McLeish



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.

Citation

Graham, R. S., Bent, J., Clarke, N., Hutchings, L. R., Richards, R. W., Gough, T., …McLeish, T. C. (2009). The long-chain dynamics in a model homopolymer blend under strong flow: small-angle neutron scattering and theory. Soft Matter, 5(12), 2383-2389. https://doi.org/10.1039/b817440g

Journal Article Type Article
Publication Date Jun 21, 2009
Deposit Date Oct 31, 2011
Journal Soft Matter
Print ISSN 1744-683X
Electronic ISSN 1744-6848
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 5
Issue 12
Pages 2383-2389
DOI https://doi.org/10.1039/b817440g
Public URL https://durham-repository.worktribe.com/output/1534949