Solvent self-diffusion dependence on the swelling degree of a hydrogel

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Hydrogels are versatile polymer networks with applications in various fields.
• Understanding water diffusion within hydrogels is crucial for predicting their behavior and performance.
• Polyacrylamide hydrogels are widely used due to their tunable properties.

Purpose of the Study:

• To investigate water mobility in homogeneously swollen polyacrylamide hydrogel beads using advanced NMR techniques.
• To determine the relationship between water self-diffusion coefficients and hydrogel network parameters.
• To explore the influence of swelling and network structure on water transport.

Main Methods:

• High-field Nuclear Magnetic Resonance (NMR) experiments.
• Pulsed gradient spin echo (PGSE) methods for diffusion measurements.
• Relaxation measurements to support theoretical models.

Main Results:

• The solvent self-diffusion coefficient was determined as a function of swelling time and polymer volume fraction.
• NMR sensitivity to hydrogel network structure was tunable by controlling diffusion probing time.
• A theoretical description based on a fast-exchange two-site model was substantiated.
• A tortuosity-porosity dependence was extracted and compared to existing regimes.
• Observed diffusion dependence on swelling corroborated the existence of a gel swelling-front.

Conclusions:

• NMR experiments provide valuable data for theoretical modeling of gel swelling.
• The study elucidates water diffusion mechanisms within polyacrylamide hydrogels.
• Findings contribute to a deeper understanding of hydrogel network dynamics and swelling phenomena.