Highly Entangled, Mechanically Robust Hydrogel Thin Films for Passive Cooling Materials via Open-Vessel Fabrication

Area of Science:

• Polymer Chemistry
• Materials Science
• Biomaterials Engineering

Background:

• Oxygen inhibition typically hinders the scalable fabrication of tough, low-hysteresis hydrogels, leading to brittle, highly crosslinked networks.
• Existing methods struggle to produce hydrogels with both high toughness and low hysteresis, limiting their practical applications.

Purpose of the Study:

• To develop an oxygen-tolerant strategy for synthesizing highly entangled (HE) polyacrylamide hydrogels.
• To enhance the mechanical properties, specifically toughness and deformability, of synthesized hydrogels.
• To explore the potential of these HE hydrogels for multifunctional applications.

Main Methods:

• Utilized a photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization strategy.
• Optimized the water-to-monomer ratio and introduced lithium chloride (LiCl) for spatial confinement.
• Synthesized HE polyacrylamide hydrogels under open-vessel conditions.

Main Results:

• Achieved a significant improvement in fracture energy (1.39 MJ/m³) and fracture strain (~900%) compared to brittle highly crosslinked (HC) controls (~50% strain).
• Incorporation of 15 wt% LiCl further increased fracture energy to 2.17 MJ/m³ while maintaining low hysteresis.
• Demonstrated rapid, scalable production of robust, transparent thin films with dual passive cooling, self-healing, and strain sensing capabilities down to -20 °C.

Conclusions:

• The developed PET-RAFT strategy enables the fabrication of highly entangled hydrogels with superior mechanical properties, overcoming oxygen inhibition.
• Spatial confinement engineering using LiCl significantly enhances hydrogel toughness and deformability.
• This versatile platform facilitates the production of multifunctional hydrogels for advanced applications, outperforming traditional crosslink-dominated materials.