期刊
MACROMOLECULES
卷 54, 期 20, 页码 9724-9738出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.macromol.1c01350
关键词
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资金
- Natural Science Foundation of China [21790343, 21873095]
- collaborative Research Program of i-JURC ICR, Kyoto University [2019-52, 2021-62]
The study found that ionomers based on sodium carboxylate or sodium sulfonate groups form networks sustained by salt aggregates, with M-n-SO3Na showing more stable aggregates compared to M-n-COONa. In nonlinear rheology, M-n-COONa exhibited larger strain during stress overshoot before showing weaker pseudo-yielding and higher fracture strains after overshoot, indicating easier reconstruction of the network. These differences are attributed to a nonuniform distribution of salt aggregate size and superbridge length in M-n-COONa, allowing for more efficient energy dissipation under strong flow conditions.
In this study, we examined the structure, linear viscoelastic (LVE) properties, and nonlinear shear and elonga-tional properties of unentangled telechelic ionomers based on either sodium carboxylate or sodium sulfonate groups, coded as M-n-COONa and M-n-SO3Na, with the number-average molecular weight M-n varying from 5 to 16 kg mol(-1). A combination of X-ray scattering and LVE data revealed that both types of ionomers form networks sustained by superbridges transiently cross-linked by salt aggregates. The aggregates were found to be more stabilized in the M-n-SO3Na ionomers than in the M-n-COONa ionomers. In addition, the X-ray scattering and LVE data suggested that the inner and end aggregates of the superbridge are equally stabilized in M-n-SO3Na, while the end aggregates are more stable in M-n-COONa. This difference in the aggregate stability in the two series of ionomers was found to have a significant effect on nonlinear rheology; namely, under the shear or elongational flow fields with the Weissenberg number Wi > 1, M-n-COONashowed a larger strain on the stress overshoot compared to M-n-SO3Na. This result suggested that the M-n-COONa ionomers can better adjust the network under flow before the overshoot. After the overshoot, the weaker pseudo-yielding and higher fracture strains were attained for M-n-COONa, suggesting that the associated network can be reconstructed more easily for M-n-COONa. All these features are attributable to a nonuniform distribution of the salt aggregate size and superbridge length of M-n-COONa, which enables more efficient energy dissipation under strong flow through fast rearrangement of the network.
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