writer：Donghua Xu and Stephen L. Craig*.
keywords：///
source：期刊
specific source：The Journal of Physical Chemistry Letters 2010, 1,1683-1686.
Issue time：2010年

Molecular theories of shear thickening and shear thinning in associative

polymer networks are typically united in that they involve a single kinetic

parameter that describes the network ; a relaxation time that is related to the

lifetime of the associative bonds. Here we report the steady-shear behavior of two

structurally identical metallo-supramolecular polymer networks, for which singlerelaxation

parameter models break down in dramatic fashion. The networks are

formed by the addition of reversible cross-linkers to semidilute entangled solutions

of poly(4-vinylpyridine) (PVP) in dimethylsulfoxide (DMSO), and they differ only in

the lifetime of the reversible cross-links. Shear thickening is observed for crosslinkers

that have a slower dissociation rate (17 s-1), while shear thinning is

observed for samples that have a faster dissociation rate (ca. 1400 s-1). The

difference in the steady shear behavior of the unentangled versus entangled

regime reveals an unexpected, additional competing relaxation, ascribed to

topological disentanglement in the semidilute entangled regime that contributes

to the rheological properties.