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Stimuli-responsive polyelectrolyte surfactant complexes for the reversible control of solution viscosity
Giuseppe Rosario Del Sorbo1,2, Daniel Clemens3, Emanuel Schneck4
1Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476 Potsdam, Germany.
Soft Matter
|March 11, 2022
Summary
Controlling surfactant hydrophobicity with pH significantly alters polyelectrolyte solution viscosity. At high pH, viscosity drops dramatically, while lower pH leads to highly viscous solutions due to surfactant-polyelectrolyte aggregation.
Area of Science:
- Polymer Science
- Surfactant Chemistry
- Materials Science
Background:
- Polyelectrolyte-surfactant interactions drive self-assembly into diverse structures.
- High solution viscosity arises from surfactant aggregates bridging polyelectrolyte chains.
- Surfactant hydrophobicity is crucial for forming these viscosity-enhancing aggregates.
Purpose of the Study:
- Investigate the mesoscopic structural changes in polyelectrolyte-surfactant systems.
- Correlate structural changes with drastic viscosity variations.
- Explore pH-controlled hydrophobicity for tunable material properties.
Main Methods:
- Small-angle neutron scattering (SANS)
- Neutron spin-echo spectroscopy (NSENS)
- System: anionic sodium monododecyl phosphate and cationic JR 400 polyelectrolyte
Main Results:
- Viscosity changes by up to two orders of magnitude with pH variation.
- At pH > 12, surfactant headgroup is doubly charged, reducing viscosity.
- At lower pH, surfactant is hydrophobic, forming aggregates and increasing viscosity to 10 Pa s.
Conclusions:
- Solution pH is a key factor in tuning polyelectrolyte-surfactant system viscosity.
- Structural analysis reveals the mechanism behind viscosity changes.
- These systems offer a modular approach to stimuli-responsive materials.
