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Updated: Jun 9, 2026
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Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions
Published on: September 7, 2018
Features Distinguishing the Flow Behavior of Polyelectrolytes with Opposite Charges in Aqueous Solutions
Suresha P Ranganath1, Manohar V Badiger2, Bernhard A Wolf2
1Polymer Science and Engineering Division, National Chemical Laboratory (NCL), Pune 411 008, India.
The Journal of Physical Chemistry. B
|June 8, 2026
Summary
The study reveals that the distinct rheological behaviors of polycations and polyanions in saline solutions stem from ion-polymer interactions, not just charge. This finding aids in tailoring polyelectrolyte properties.
Area of Science:
- Polymer Science and Engineering
- Physical Chemistry
- Materials Science
Background:
- Polyelectrolytes exhibit complex rheological properties in solution, influenced by factors like molecular weight, charge density, and ionic strength.
- Understanding the interplay between polymer structure, counter-ions, and solvent is crucial for predicting and controlling solution behavior.
Purpose of the Study:
- To investigate the solution viscosity and shear-overlap parameters of a polycation (PAPTMAC-Cl) and a polyanion (PSS-Na) across varying NaCl concentrations.
- To elucidate the underlying mechanisms responsible for the observed differences in rheological behavior between the polycation and polyanion.
- To explore the applicability of the Hard Soft Acid Base (HSAB) theory in explaining these differences and guiding polyelectrolyte property tailoring.
Main Methods:
- Measurement of solution viscosities for poly((3-(acrylamido)propyl)trimethylammonium chloride) (PAPTMAC-Cl 7.8) and poly(styrenesulfonate sodium) (PSS-Na 75.6) in water with varying NaCl concentrations at 25 °C.
- Calculation of intrinsic viscosity and shear-overlap parameters (Σ) as a function of polymer concentration (c).
- Analysis of results using the Hard Soft Acid Base (HSAB) approach.
Main Results:
- The intrinsic viscosity of PAPTMAC-Cl was significantly higher than that of PSS-Na, despite its lower molecular weight.
- Shear-overlap parameters (Σ) showed distinct concentration dependencies: maxima for PAPTMAC-Cl and inflection points for PSS-Na at low salinities, becoming linear at high salinities.
- The crossover salinity (Σcrov) was consistently higher for the polycation than the polyanion.
Conclusions:
- The observed differences in rheological behavior are attributed to the specific ion-polymer interactions (soft NR4+ with hard Cl- for PAPTMAC-Cl; hard RSO3- with hard Na+ for PSS-Na), rather than just the charge polarity.
- The HSAB approach provides a valuable framework for understanding these interactions and predicting polyelectrolyte solution properties.
- This insight enables targeted modification of polyelectrolyte structures and counter-ion choices for precise control over rheological performance in saline environments.
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