Revisiting the strain-induced softening behaviour in hydrogels

Area of Science:

• Materials Science
• Polymer Physics
• Soft Matter

Background:

• Strain-induced softening in hydrogels is commonly attributed to network structure breakage.
• Understanding the mechanisms behind hydrogel mechanical behavior is crucial for material design.

Purpose of the Study:

• To investigate alternative mechanisms for strain-induced softening in hydrogels.
• To challenge the conventional explanation of network breakage as the sole cause of softening.

Main Methods:

• Utilized a stress-strain relationship derived from a coarse-grained model.
• Analyzed the energy-related contribution to the elastic modulus.
• Compared theoretical predictions with experimental data from various hydrogels.

Main Results:

• Demonstrated that network rupture is not essential for observing softening behavior.
• Linked the decrease in differential modulus (K(T,γ)) to energy-related contributions.
• Showed that polymer-solvent interactions can drive softening.

Conclusions:

• Softening in hydrogels can arise from polymer-solvent interactions, not solely from network damage.
• The proposed model provides a new perspective on hydrogel mechanics.
• Findings are validated by experimental data from tetra-PEG hydrogels and others.