Manipulating\nToughness and Microstructure in Polyelectrolyte\nComplex Hydrogels with Competitive Surfactant Micelles

Polyelectrolyte complex (PEC) hydrogels provide a promising\nstrategy\nto develop a class of physically cross-linked networks characterized\nby exceptional toughness and self-healing properties. However, the\nprecise control of the microstructure and the enhancement of mechanical\nproperties still pose challenges in the field of PEC hydrogels. Herein,\nwe propose a strategy to manipulate the structure of PEC with competitively\ncharged surfactant micelles, leveraging the spatially confined surface\ncharge and excluded volume effects to overcome coacervation issues\nassociated with the PEC, thus achieving a simple one-step preparation\nof macroscopically uniform and tough PEC hydrogels. Specifically,\npolyelectrolyte complex/surfactant micelle (PEC-SM) hybrid hydrogels\nwere prepared by one-step copolymerization of chitosan (CS)/acrylic\nacid/cetyltrimethylammonium bromide (CTAB) micelles. The content of\nCTAB micelles was found to continuously modulate both the structure\nand the mechanical properties of the resulting PEC-SM hydrogel network.\nOn one hand, reversible deformation-recovery behavior exhibited by\nCTAB cavity micelles through hydrophobic interactions efficiently\ndissipates energy; on the other hand, competition between CS chains\nand CTAB micelles for electrostatic binding sites with poly(acrylic\nacid), along with excluded volume effects of CTAB micelles, imparts\na hierarchical structure upon the PEC-SM hydrogel. Rheology provided\ndetailed insights into the viscoelastic behaviors of PEC-SM hydrogels\nat varying CTAB concentrations. The intermolecular interaction and\nheterogeneous network structure of physically cross-linked PEC-SM\nhydrogels with CTAB micelles were elucidated by solid-state nuclear\nmagnetic resonance (NMR) spectroscopy. On the basis of rheology and\nNMR results, complemented by other characterization analyses, the\nphysical illustration of the PEC-SM hybrid hydrogel network structure\nregulated by competitive surfactant micelles is presented. This work\noffers valuable in-depth insight into polyelectrolyte complexation\nand provides a foundation for the development of robust PEC hydrogel\nmaterials.