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Oscillatory structural forces between charged interfaces in solutions of oppositely charged polyelectrolytes
Katarzyna Kubiak1, Plinio Maroni, Gregor Trefalt
1Department of Inorganic and Analytical Chemistry, University of Geneva, Sciences II, 30 Quai Ernest-Ansermet, 1205 Geneva, Switzerland. michal.borkovec@unige.ch.
Soft Matter
|October 20, 2020
Summary
Oscillatory forces between silica particles in polyelectrolyte solutions are common, even with opposite charges. These forces reveal polyelectrolyte solution structuring, with scaling exponents changing with concentration.
Area of Science:
- Colloid and surface science
- Polymer physics
- Soft matter physics
Background:
- Forces between charged particles in solution are crucial for understanding material properties.
- Polyelectrolytes significantly alter colloidal interactions.
- Previous studies focused on like-charged systems, leaving oppositely charged systems less explored.
Purpose of the Study:
- To investigate the forces between oppositely charged silica particles and cationic polyelectrolytes.
- To determine the role of polyelectrolyte concentration on interparticle forces.
- To elucidate the underlying mechanisms responsible for observed oscillatory force profiles.
Main Methods:
- Atomic force microscopy (AFM) was employed to measure forces between micron-sized silica particles.
- Experiments were conducted in aqueous solutions with varying concentrations of cationic polyelectrolytes.
- Force profiles were analyzed to extract oscillatory behavior and scaling laws.
Main Results:
- Damped oscillatory force profiles were systematically observed at higher polyelectrolyte concentrations (few g L-1).
- The oscillation wavelength decreased with increasing polyelectrolyte concentration.
- Universal power-law dependencies were found for normalized wavelength and concentration, with scaling exponents of 1/3 and 1/2 in dilute and semi-dilute regimes, respectively.
Conclusions:
- Oscillatory forces are a general phenomenon in polyelectrolyte solutions, including oppositely charged systems.
- These forces are linked to the structuring of polyelectrolyte solutions.
- Charge reversal on silica surfaces due to polyelectrolyte adsorption explains the similarity between oppositely and like-charged systems.
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