Modeling deswelling, thermodynamics, structure, and dynamics in ionic microgel suspensions

Area of Science:

• Soft Matter Physics
• Colloid Science
• Polymer Chemistry

Background:

• Ionic microgels swell in good solvents due to electrostatic and elastic forces.
• Particle crowding induces microion redistribution, leading to microgel deswelling.
• Deswelling significantly impacts inter-particle interactions and overall suspension properties.

Purpose of the Study:

• To theoretically investigate the effects of crowding on ionic microgel suspensions.
• To model thermodynamic, structural, and dynamic properties of deswelling microgels.
• To develop a bottom-up approach for predicting crowded microgel suspension behavior.

Main Methods:

• Modeling microgels as permeable colloidal spheres with fixed charge.
• Employing Flory-Rehner theory for elastic and solvent-interaction free energies.
• Utilizing mean-field methods to calculate crowding-dependent microgel radius and net charge.
• Calculating effective pair potentials, osmotic pressure, and pair distribution functions.
• Incorporating hydrodynamic interactions for dynamic property calculations.

Main Results:

• Deswelling mildly enhances self- and collective diffusion.
• Osmotic pressure increases with deswelling.
• Suspension viscosity decreases, while the crystallization point shifts to higher concentrations.
• Crowding effects on thermodynamic, structural, and dynamic properties were quantified.

Conclusions:

• Crowding-induced deswelling is a key factor governing ionic microgel suspension behavior.
• The theoretical framework provides efficient computation of suspension properties from single-particle characteristics.
• This study offers insights into designing and controlling soft matter systems.