Dynamics of entangled H-polymers: Theory, rheology, and neutron-scattering

Citation
Tcb. Mcleish et al., Dynamics of entangled H-polymers: Theory, rheology, and neutron-scattering, MACROMOLEC, 32(20), 1999, pp. 6734-6758
Citations number
48
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
MACROMOLECULES
ISSN journal
0024-9297 → ACNP
Volume
32
Issue
20
Year of publication
1999
Pages
6734 - 6758
Database
ISI
SICI code
0024-9297(19991005)32:20<6734:DOEHTR>2.0.ZU;2-2
Abstract
We present experiments and theory on the melt dynamics of monodisperse enta ngled polymers of H-shaped architecture. Frequency-dependent rheological da ta on a series of polyisoprene H-polymers are in good agreement with a tube model theory that combines path-length fluctuation (like that of star poly mer melts) at high frequency, with reptation of the self-entangled "cross-b ars" at low frequencies (like that of linear polymer melts). We account exp licitly for mild polydispersity. Nonlinear step-strain and transient data i n shear and extension confirm the presence of a relaxation time not seen in linear response, corresponding to the curvilinear stretch of the cross-bar s. This time is very sensitive to strain due to the exponential, dependence of the branch-point friction constants on the effective dangling path leng th. Strain-induced rearrangements of the branch points are confirmed by sma ll-angle neutron scattering (SANS) on stretched and quenched partially deut erated samples. We develop an extension of melt-scattering theory to deal w ith the presence of deformed tube variables to interpret the SANS data.