Swelling of micro-hydrogels with a crosslinker gradient

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Micro-hydrogels (microgels) exhibit non-uniform polymer density due to heterogeneous crosslinker distribution.
• Understanding microgel morphology is crucial for predicting their structural and rheological properties.
• Existing models often simplify network structure, limiting predictive power.

Purpose of the Study:

• To develop a computational model for predicting microgel morphology and density profiles.
• To investigate the impact of non-uniform crosslinker distribution on microgel structure.
• To validate the model against experimental data, specifically SAXS.

Main Methods:

• Utilized a Flory-Rehner inspired model for highly swollen polymer networks.
• Performed ab initio calculations accounting for non-uniform crosslinker distribution during synthesis.
• Applied the model to poly(N-isopropylacylamide) (PNIPAM) microgels, with applicability to other architectures.

Main Results:

• Successfully recovered a single-particle density profile for microgels.
• The calculated density profile showed close agreement with experimental Small-Angle X-ray Scattering (SAXS) data.
• Confirmed the presence of significant-sized dangling polymer ends on the surface of cross-linked particles.

Conclusions:

• The computational approach accurately models microgel internal structure based on synthesis conditions.
• The findings provide a bottom-up understanding of microgel properties.
• The study highlights the importance of considering non-uniform crosslinker distribution for accurate microgel characterization.