期刊
JOURNAL OF CHEMICAL PHYSICS
卷 138, 期 12, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.4769253
关键词
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资金
- Royal Society
- Engineering and Physical Sciences Research Council (U.K.) EPSRC [EP/E030173, EPSRC/E5336X/1]
- European Research Council under the European Union's Seventh Framework Programme [279365]
- National Science Foundation (NSF) [DMR 0906587]
- Engineering and Physical Sciences Research Council [EP/E05336X/2] Funding Source: researchfish
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [906587] Funding Source: National Science Foundation
- EPSRC [EP/E05336X/2] Funding Source: UKRI
Glassy polymers show strain hardening: at constant extensional load, their flow first accelerates, then arrests. Recent experiments under such loading have found this to be accompanied by a striking dip in the segmental relaxation time. This can be explained by a minimal nonfactorable model combining flow-induced melting of a glass with the buildup of stress carried by strained polymers. Within this model, liquefaction of segmental motion permits strong flow that creates polymer-borne stress, slowing the deformation enough for the segmental (or solvent) modes then to re-vitrify. Here, we present new results for the corresponding behavior under step-stress shear loading, to which very similar physics applies. To explain the unloading behavior in the extensional case requires introduction of a crinkle factor describing a rapid loss of segmental ordering. We discuss in more detail here the physics of this, which we argue involves non-entropic contributions to the polymer stress, and which might lead to some important differences between shear and elongation. We also discuss some fundamental and possibly testable issues concerning the physical meaning of entropic elasticity in vitrified polymers. Finally, we present new results for the startup of steady shear flow, addressing the possible role of transient shear banding. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769253]
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