Dynamic model of monovalent-divalent cation exchange in polyelectrolyte gels

Area of Science:

• Polymer Science
• Physical Chemistry
• Materials Science

Background:

• Charged polymer gels exhibit complex volume transitions influenced by ion interactions.
• Understanding these transitions is crucial for applications in soft robotics, drug delivery, and sensors.

Purpose of the Study:

• To develop and validate a multicomponent model for predicting the behavior of charged polymer gels.
• To investigate the influence of mono- and divalent cations on gel swelling and ion partitioning.

Main Methods:

• A multicomponent continuum model was developed, incorporating conservation laws and constitutive relations for polymer chains, water, and ions.
• The model links ion exchange to gel volume via a linear relationship between the polymer-solvent interaction parameter and adsorbed divalent cation concentration.
• Model predictions were compared against experimental measurements on sodium polyacrylate gels.

Main Results:

• The model successfully reproduced the dynamics of gel swelling and deswelling.
• Semiquantitative agreement was achieved for the ion partitioning coefficient.
• The model accurately predicted the effect of cross-link density on gel volume transitions.

Conclusions:

• The multicomponent coarse-grained continuum modeling approach provides a robust framework for quantitative predictions of polymer gel behavior.
• This modeling strategy is effective for macroscopic length and timescales, capturing critical volume transitions in ionic environments.