Rheological Properties of Concentrated Sodium Polystyrenesulfonate in Aqueous Salt Solutions
We study the conformational and flow properties of sodium polystyrenesulfonate in aqueous NaCl solutions in the high polymer, high added-salt region using rheology and small angle neutron scattering (SANS). For low salt concentrations, the specific viscosity decreases with added salt as expected. At very high salt, however, the specific viscosity is found to rapidly increase with increasing added-salt concentration (cs). This indicates that addition of salt modifies the system in ways other than simply decreasing the electrostatic screening length. Beyond a critical shear stress of around 400 Pa, independent of molar mass, solutions display strong shear thickening reminiscent of shear-induced gelation. Scaling laws for the zero shear rate viscosity and critical shear rate with molar mass, polymer and added-salt concentration are established and compared to similar behavior observed for other systems. SANS experiments using the zero-average-contrast technique reveal that the chain size monotonically decreases with increasing added salt concentration, indicating that the increases in specific viscosity cannot be assigned to chain expansion. Our results indicate that NaPSS, usually thought to be a model polyelectrolyte system, displays complex and unexpected rheological behavior when both the polymer and added salt concentration approach the molar range, where the Debye screening length becomes smaller than the Bjerrum length.
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| Work Title | Rheological Properties of Concentrated Sodium Polystyrenesulfonate in Aqueous Salt Solutions |
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| License | CC BY 4.0 (Attribution) |
| Work Type | Article |
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| Publication Date | July 20, 2024 |
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| Deposited | October 22, 2024 |
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