Pre-Freezing-Assisted Wet Annealing Yields Mechanically Robust Hydrogels with Tunable Water Content.

Area of Science:

• Materials Science
• Polymer Chemistry

Background:

• Developing hydrogels with simultaneously enhanced mechanical properties (strength, stretchability, toughness, fatigue resistance) and tunable water content is challenging.
• Conventional methods often struggle to balance these properties, limiting hydrogel applications.

Purpose of the Study:

• To introduce a universal "pre-freezing-assisted wet-annealing" strategy for poly(vinyl alcohol) (PVA) hydrogels.
• To achieve simultaneous enhancement of multiple hydrogel properties, including mechanical strength, stretchability, toughness, fatigue resistance, and tunable water content.

Main Methods:

• A dual-phase processing strategy involving pre-freezing and wet-annealing was employed.
• Pre-freezing controlled phase separation for high water content gelation from low-concentration solutions.
• Wet-annealing induced polymer conformational rearrangement for network densification and crystallite formation.

Main Results:

• The developed PVA hydrogels demonstrated exceptional mechanical properties: tensile strength (11.9 MPa), fracture strain (1275.4%), toughness (80.2 MJ m^-3), and fracture energy (21.8 kJ m^-2).
• The hydrogels exhibited a high fatigue threshold (902.8 J m^-2) and tunable water content (55-88%).
• Characterizations revealed enhanced crystallinity and intensified hydrogen bonding, contributing to improved performance.

Conclusions:

• The "pre-freezing-assisted wet-annealing" strategy is a versatile paradigm for engineering high-performance hydrogels.
• These hydrogels show superior fatigue and swelling resistance, low friction, and potential for underwater load-bearing applications.
• The synergistic effect of phase transition and macromolecular reorganization offers a new pathway for advanced hydrogel development.