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Originally published in Science Express on 2 October 2008
Science 31 October 2008:
Vol. 322. no. 5902, pp. 720 - 724
DOI: 10.1126/science.1157945
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Reports

Molecular Confinement Accelerates Deformation of Entangled Polymers During Squeeze Flow

Harry D. Rowland,1 William P. King,1 John B. Pethica,2 Graham L. W. Cross2*

The squeezing of polymers in narrow gaps is important for the dynamics of nanostructure fabrication by nanoimprint embossing and the operation of polymer boundary lubricants. We measured stress versus strain behavior while squeezing entangled polystyrene films to large strains. In confined conditions where films were prepared to a thickness less than the size of the bulk macromolecule, resistance to deformation was markedly reduced for both solid-glass forging and liquid-melt molding. For melt flow, we further observed a complete inversion of conventional polymer viscosity scaling with molecular weight. Our results show that squeeze flow is accelerated at small scales by an unexpected influence of film thickness in polymer materials.

1 Department of Mechanical Science and Engineering, University of Illinois, Urbana, IL 61801, USA.
2 School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, Dublin 2, Ireland.

* To whom correspondence should be addressed. E-mail: graham.cross{at}tcd.ie

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Science. ISSN 0036-8075 (print), 1095-9203 (online)