Osmotic Swelling Behavior of Ionic Cylindrical Microgels

Ionic microgels are cross-linked polymeric networks that ionize and swell in a good solvent. The swelling behavior of the particles can be tuned by adjusting temperature, pH, and ionic strength, enabling applications to drug delivery and tissue engineering. Unlike spherical microgels, cylindrical microgels can swell in both radial and axial directions. Equilibrium swelling can be triggered by varying the balance between electrostatic and gel contributions to the osmotic pressure inside and outside of the particles [1, 2]. Within a cell model, we derive an exact statistical mechanical theorem for the electrostatic osmotic pressure of a cylindrical microgel to study the dependence of microion distribution and osmotic pressure on equilibrium size. To validate the theorem, we implemented Poisson-Boltzmann theory and molecular dynamics simulations. Combining our theorem with Flory-Rehner theory of polymer networks, we predict radial and axial equilibrium swelling ratios of cylindrical microgels as a function of salt concentration. Our results can help guide the design of smart, responsive particles.

[1] A. R. Denton and M. O. Alziyadi, J. Chem. Phys. 151, 074903 (2019).
[2] A. R. Denton and Q. Tang, J. Chem. Phys. 145, 164901 (2016).