Bridging like-charged macroions through long divalent rodlike ions.
Sylvio May1, Ales Iglic, Jurij Rescic
1Department of Physics, North Dakota State University, Fargo, ND 58105-5566, USA.
The Journal of Physical Chemistry. B
|January 22, 2008
Summary
Like-charged macroions attract due to ion structure. Rodlike ion models predict attraction and overcharging, highlighting the importance of ion shape in electrolyte solutions.
Area of Science:
- Physical Chemistry
- Colloid Science
- Statistical Mechanics
Background:
- Like-charged macroions typically repel in electrolyte solutions.
- Inter- and intramolecular correlations in mobile ions can induce attraction.
- Poisson-Boltzmann theory can predict attraction when ion structure is considered.
Purpose of the Study:
- To investigate attraction between like-charged macroions in aqueous solutions.
- To explore the role of mobile divalent ions with internal structure (rodlike ions).
- To analyze the impact of ion shape and correlations on macroion interactions.
Main Methods:
- Application of variational theory to a symmetric 2:2 electrolyte of rodlike ions.
- Derivation of an integro-differential equation for arbitrary rod lengths.
- Numerical solutions and comparison with Monte Carlo simulations.
Main Results:
- Electrostatic attraction emerges above a critical rod length, distinct from depletion forces.
- A bridging mechanism involving rodlike ions facilitates macroion association.
- Overcharging (charge over-compensation) is observed for sufficiently long rodlike ions.
Conclusions:
- The internal structure of mobile ions, particularly their rodlike shape, is crucial for understanding macroion interactions.
- Results emphasize the significance of condensing agents like polyamines and peptides.
- Theoretical predictions align with simulation data, validating the model.
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