Polyelectrolytes induce water-water correlations that result in dramatic viscosity changes and nuclear quantum
1Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Science Advances
|February 18, 2020
Summary
Long-range ion electric fields significantly impact water correlations and viscosity in polyelectrolyte solutions. These effects, particularly pronounced with heavy water (D2O), highlight the importance of nuclear quantum effects in aqueous systems.
Area of Science:
- Physical Chemistry
- Solution Chemistry
- Materials Science
Background:
- Ions interact with water through short-ranged ion-dipole forces.
- A previously identified Jones-Ray effect shows ions can influence water structure over longer ranges, affecting surface tension.
- The extent and impact of these long-range electrostatic interactions on solution properties are not fully understood.
Purpose of the Study:
- To investigate the substantial contribution of long-range electrostatic interactions to molecular and macroscopic properties in aqueous polyelectrolyte solutions.
- To elucidate the role of these interactions in solution viscosity and water-water correlations.
- To explore the influence of isotopic substitution (H2O vs. D2O) on these phenomena.
Main Methods:
- Femtosecond elastic second harmonic scattering (fs-ESHS) to probe water-water correlations.
- Viscosity measurements across a range of polyelectrolyte concentrations.
- Comparative studies using both light water (H2O) and heavy water (D2O).
Main Results:
- fs-ESHS revealed strong long-range electrostatic interactions increasing water-water correlations in polyelectrolyte solutions.
- A significant reduction in viscosity, spanning over two orders of magnitude with concentration, was observed.
- Using D2O instead of H2O shifted fs-ESHS and viscosity profiles and altered maximum viscosity, indicating nuclear quantum effects.
Conclusions:
- Long-range electrostatic interactions significantly influence water structure and dynamics in polyelectrolyte solutions.
- Observed phenomena, including isotopic effects, cannot be explained by mean-field approximations and strongly suggest the involvement of nuclear quantum effects.
- These findings necessitate a revised understanding of ion-water interactions beyond simple short-range forces.
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