Swelling Behavior and Structure of Binary Mixtures of Ionic Microgels

Ionic microgels are soft, responsive colloids that exhibit unique swelling behavior due to their osmotic pressure-driven changes in volume. When dispersed in solution, microgels absorb solvent and can become charged by releasing counterions. Understanding the osmotic pressure and swelling behavior of ionic microgels is crucial for designing and optimizing applications, e.g., in drug delivery, tissue engineering, and biosensing. For binary mixtures of ionic microgels that carry fixed charges on their surfaces, we derive effective electrostatic interactions. We model steric interparticle interactions via Hertz elastic pair potentials and single-microgel swelling via Flory-Rehner theory of polymer networks. Within this coarse-grained modeling framework [1-3], we perform Monte Carlo simulations, with trial microgel size changes, to compute equilibrium swelling ratios and radial distribution functions. For size- and charge-asymmetric mixtures, we observe unusual self-healing behavior, in qualitative agreement with experiments [4]. Our results can illuminate fundamental principles governing swelling behavior and structural properties of ionic microgel mixtures, offering a foundation for designing novel responsive materials.

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