Counterion-Induced Swelling of Ionic Microgels
arXiv:1610.01180 · doi:10.1063/1.4964864
Abstract
Ionic microgel particles, when dispersed in a solvent, swell to equilibrium sizes that are governed by a balance between electrostatic and elastic forces. Tuning of particle size by varying external stimuli, such as H, salt concentration, and temperature, has relevance for drug delivery, microfluidics, and filtration. To model swelling of ionic microgels, we derive a statistical mechanical theorem, which proves exact within the cell model, for the electrostatic contribution to the osmotic pressure inside a permeable colloidal macroion. Applying the theorem, we demonstrate how the distribution of counterions within an ionic microgel determines the internal osmotic pressure. By combining the electrostatic pressure, which we compute via both Poisson-Boltzmann theory and molecular dynamics simulation, with the elastic pressure, modeled via the Flory-Rehner theory of swollen polymer networks, we show how deswelling of ionic microgels with increasing concentration of particles can result from a redistribution of counterions that reduces electrostatic pressure. A linearized approximation for the electrostatic pressure, which proves remarkably accurate, provides physical insight and greatly eases numerical calculations for practical applications. Comparing with experiments, we explain why soft particles in deionized suspensions deswell upon increasing concentration and why this effect may be suppressed at higher ionic strength. The failure of the uniform ideal-gas approximation to adequately account for counterion-induced deswelling below close packing of microgels is attributed to neglect of spatial variation of the counterion density profile and the electrostatic pressure of incompletely neutralized macroions.
arXiv comment11 pages, 7 figures
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Cited by in corpus (8)
- Numerical insights on ionic microgels: structure and swelling behaviour
- Modeling deswelling, thermodynamics, structure, and dynamics in ionic microgel suspensions
- Ionic Size Effects on the Poisson-Boltzmann Theory
- Cell Model Approaches for Predicting the Swelling and Mechanical Properties of Polyelectrolyte Gels
- Osmotic Pressure and Swelling Behavior of Ionic Microcapsules
- Osmotic Pressure of Permeable Ionic Microgels: Poisson-Boltzmann Theory and Exact Statistical Mechanical Relations in the Cell Model
- Osmotic Swelling Behavior of Surface-Charged Ionic Microgels
- Interface-induced hysteretic volume phase transition of microgels: simulation and experiment