A multiphasic model for the volume change of polyelectrolyte hydrogels

Area of Science:

• Materials Science
• Chemical Engineering
• Biomedical Engineering

Background:

• Polyelectrolyte hydrogels exhibit significant volume changes in response to environmental stimuli.
• Understanding the driving forces and kinetics of hydrogel swelling is crucial for their application.

Purpose of the Study:

• To derive and validate a multiphasic model for polyelectrolyte hydrogel volume change.
• To investigate the influence of external salt concentration on hydrogel swelling kinetics.
• To differentiate swelling mechanisms in ordinary versus fast-response hydrogels.

Main Methods:

• Derivation of a multiphasic model incorporating conservation of mass and momentum.
• Modeling the driving forces as gradients of chemical/electrochemical potentials.
• Finite element method simulation of free swelling in spherical hydrogels immersed in salt solutions.

Main Results:

• The model accurately predicts hydrogel swelling from the surface inward as external salt concentration decreases.
• Swelling kinetics are shown to be dependent on the frictional coefficient between the polymer network and water.
• Two distinct swelling regimes identified: polymer network diffusion-controlled for ordinary hydrogels and ionic diffusion-controlled for fast-response hydrogels.

Conclusions:

• The developed multiphasic model provides a robust framework for analyzing polyelectrolyte hydrogel swelling.
• The study highlights the critical role of ionic diffusion and polymer network dynamics in determining hydrogel response times.
• Findings offer insights for designing hydrogels with tailored swelling behaviors for specific applications.